The Mighty Stu very successfully prepped for several bodybuilding contests while working in a school. You're as limited as your preparation allows. Can pack and bring a lunch?
I meant one bigass shake in the morning - like a typical breakfast blender bomb with milk, fruit, protein powder, maybe some peanut butter or other goodies - and then lunch and dinner, not really having several giant shakes through the day.
And anyhow, the "how much protein per meal" is a theory that's been around for a while and there's no one overwhelmingly-agreed on answer. But the body can certainly handle a "decent" amount of protein per meal, especially if digestion is optimized and especially when your body's putting the protein to work by recovering from/adapting to weight training. This article talks a bit about it:
So, you could easily shoot for protein in the 40-60g range per meal. That's shouldn't be tough to get from whole foods - two cans of tuna, two chicken breasts, 5 or 6 hard-boiled eggs, even a bag of beef jerky has about 45g.
I'm not "against" protein shakes by any means, I'm just think there are options other than a predominantly-liquid diet for your current situation. But if that's what works, and I do mean works as in seeing the results you want, then that's what works for you.