Wellll....re the soup thing, I must admit that for the last several months I've done something similar, as I'm on a very restricted weight loss program and only allowed to eat the meals provided on the program. I don't think my mom and daughter should be deprived of eating out, though, so when we've gone out, I've let the waitperson know I won't be ordering food for myself, but will order a diet soda, a pot of hot water and a bowl to mix my soup. Mind you, I'm usually buying at least one other person's meal, sometimes two other people, would gladly pay any service charge for the hot water (but have never been charged) and I add a few extra dollars to the tip.
At none of the places I've done this (a couple of them pretty fancy) has the waitperson objected or even acted surprised. They've been very accommodating and helpful. I'd imagine this comes up once in awhile, where someone in a party has a dietary restriction or has already eaten and is just having a drink or something like that.
Of course, walking in and letting the waitperson know that you consider the restaurant's prices outrageous and that your intent is to take up a table without ordering anything, that's probably not going to go well.