TL;DR: Smile and nod (wave your hand) instead of speaking.
I beg to differ. I find this sentence the most important of your question (since this is usually my case as well):
I just want to eat in peace and not have to answer your question with my mouth full, or at all.
There is a better way
Instead of instructing the service personnel (often there are more waiters) in advance, that you require a special treatment which is at odds with how they serve hundreds of other people every day (and which, being of certain decency, you surely must reflect with a huge tip!) you find yourself a useful habit which is very simple to go by and works everywhere (even when you don't speak local language!).
What to do
You do it like this: put on a smile with lips closed together, position your hand causally about five inches (12 centimeters) above the table, palm down, and move it about the same distance laterally in the direction of the hand (right hand from left to right), than you fold your palm again, and continue eating without being forced to any socially unacceptable or uncomfortable position.
Note: Smile alone goes a long way, which is useful in social situations.
Etiquette, a.k.a. not forcing other people to awkward or uncomfortable situations, should extend to service as well. What is important to mention is that once you form a habit of instructing the waiter in advance that you wish not to be disturbed, you may very quickly grow into yet another habit of expecting the waiters to understand your request even in a perhaps complicated situation , which may lead to misunderstanding and awkward situations (complicated for you: you say only half of what you mean and confuse the waiter, complicated for the waiter: you ask nicely yet still disturb said water's flow or concentration).