Tom's all over it (as usual). Pretty much the gas block and the buffer are doing the heavy lifting when it comes to ejection patterns (short of powder charge). That's pretty much the only way that you're going to change how these beasts "spit out" the empties.
As far as cans (since you're joining the club). For what it's worth, I haven't had any issues running 5.56 rifles suppressed. They just don't seem to care if they're suppressed or not. But, for 7.62 rifles, you're probably going to want to change out your gas block. The back pressure is noticeably higher. Choking down the gas is damn near mandatory. Otherwise your headed towards some kind of malfunction from either the extra heat or pressure that's created. And it's never going to hurt to run a heavy buffer in them also. If nothing else, they help smooth out the recoil.
Also, get ready for the extra amount of cleaning that's needed once you start running the can. <laughs>