It's like you said, the G/C/G spots are almost inter-changeable. Meredith would play G in some injury scenarios.
The Bills have had no one behind their starters all offseason. You think they're suddenly gonna bring in some help with one week to go? No way does that guy learn the system and blocking scheme that fast.
All I'm saying is, with the season opener one week away I don't think the Bills will bring in any O-Lineman. I think they'd rather have extra LBs and DBs for ST purposes. And should there be an OL injury, then they'll address it right then and there and bring in someone off the street. This is how Buddy appears to be managing his roster. And it makes sense. If there was a decent O-Lineman available you have to believe that Buddy, as a football guy, would've already brought him in.