Pete and John like Patrick Lewis and I don't expect to see a FA signing at C, except possibly as depth. Funny how so many people keep talking about LJP and omitting or barely mentioning Patrick Lewis. I'm a huge LJP fan, but Patrick Lewis won the job after learning the offense. Our record with Lewis playing center was pretty darn good (6-0 I think someone said) so I just don't see a crisis or really even a question mark.
I believe Pete and John have already pencilled Patrick Lewis in as the starting center for 2015, with LJP in the mix as a backup C/Guard, and have pretty much crossed Center off their worry list; in fact, their confidence in Lewis and LJP as a backup allowed them to pull the trigger on the Jimmy Graham deal. I do expect PC/JS will choose a C/G or two in the draft, but that's a 2016/2017 "always compete" plan on their part, and it might be a late-round project rather than a high or mid round projected starter.