There's no general-case way to answer this question because your friend's aversion could be caused by any number of things, alone or together. Specific advice might be different if he's merely shy compared with, say, having some sort of social neurosis. Additionally, we can't really gauge how receptive he'll be to any sort of help from you.
I think that it will be important to talk to your friend, openly and honestly, about what he wants, why he's averse, and whether or not he's interested in overcoming obstacles to getting what he wants. He may not be, and you can't make him. And even if he is, it might feel too intense to him to approach strangers with a wingman right away.
However, I was very shy when younger (not just with women), and here are some ideas that helped me, as well as some conclusions that I reached in retrospect.
1. Sometimes things won't go well. But sometimes they will.
This is a hard one to internalize, but it's true. No matter who the people involved are, or the exact situation, sometimes people will be uninterested, unreceptive, or even outright hostile. Sometimes conversations will sputter to a halt. Sometimes things will be awkward. These undesirable situations (and many more!) will happen, sometimes. Conversely, sometimes things will go really well! But it's important to be ready for things not to work out so that you won't dwell on shock or surprise, or associate making an effort with failure.
2. Recognize that stakes are low.
Going to a place that's not one of your regular hangouts and talking to a someone that you'll likely never see again means that there is nothing much at stake. Even a terrible interaction won't really have any impact outside of his memory, and so with (1) above in mind even if things go poorly on a given attempt he really isn't worse off. So there's not much reason to avoid interaction as you're not better off for having done so.
3. "Failure" isn't the only reason things might not work out.
Sometimes conversations fall flat because two people have few (or no) common interests, and so they have nothing to talk about. Sometimes people have very different styles of communication, which causes conversations between them to lean towards being awkward or disjointed. There are lots of reasons things might not work out the way your friend might hope.
This does not necessarily mean that he did a bad job at interacting with them, or that he failed in any meaningful way. Sometimes people just don't get along smoothly, and if that turns out to be the case it's unlikely that more of a relationship would be all that enjoyable for either person. It happens, and it's better to find someone whose company he might enjoy more instead of trying to force an interaction to continue.
4. You're not moving towards a goal, you are building a relationship.
This one was huge for me. Approaching a woman with the specific goal of getting a date made me feel a huge amount of pressure, in every element of an interaction, all the time. It also changes the impression that I make. It's odd to try to leap from being strangers to going on a date, and while some people can do that successfully I wouldn't bet on your friend being one of them. If my perspective is that I am getting to know someone I feel much more relaxed, conversations are much more pleasant and fun, and I'm also much more likely to determine if I would even want a romantic date with a person. And, if I do end up wanting that, it seems much more likely to happen when that has not been my goal from even before the conversation started.
5. This is something that you learn to do, not something that you start out great at.
Obviously some people have natural talent for socializing, flirting, etc. That does not describe me, and it sounds like it does not describe your friend, either. So it's important to note that if you are not as good as you would like in this area your only real option to improve is to develop better skills through practice. That means awkward starts, mistakes, and problems. But it also means fewer of those as time goes on, and more success instead. Whether or not a given interaction goes the way your friend wants, it's important to bear in mind that next time can be better.
6. You have to learn to walk before you can run.
If this situation, as a whole, is really intimidating it will be helpful to break things down a bit. Maybe a lot. So instead of having a mindset of "I'm getting a date tonight", it might be more appropriate to have a goal like "I'm going to have a conversation with a stranger for five minutes tonight". If that's still too big, maybe even "I'm going to casually smile and say hello to someone". With practice, these smaller steps can feel more natural and comfortable, providing a foundation for the next goal. My more socially-confident friends had a hard time understanding why I couldn't just follow their leads when they were my "wingmen", but I was nervous about every single part of interactions in a lot of situations. I had to practice them individually until I had enough confidence and experience to casually string them together in a "normal" interaction.
tl;dr
Without a lot of natural talent, more skill comes from practice and effort. If he's so averse to interacting with people that practicing is difficult then a different mindset is likely appropriate. With the right mindset it still takes effort, time, and the will to endure and overcome mistakes to improve. But improvement is absolutely possible.
Assuming that he does want to improve, as his friend your best move is probably to help him develop and internalize a better mindset, and then practice until his relevant social skills develop to the level he wants.
