Have we seen Peter use any powers that he could have only gotten from being near Sylar?
I'm not thinking of any off the top of my head (but I'm crap at details like that.)
If not, then my theory is that by being near Sylar he wouldn't have gotten any of the abilities that Sylar sucked out of brains because those aren't Sylar's powers. What Peter would have gotten from him is the brain sucking power, which he'd never use, of course.