Let's assume JP is out the full 12 weeks. That would, conservatively, put him back at full practice around November 15th. That means there are still 7 games left. And depending on the Bills record/situation going into the last 3 weeks, JP could get in some playing time.
If they put him on IR, he can't practice with the team at all. If they leave him active, at lest he can be in on all of the meetings, film sessions and working out to some extent.
Also, Zolman is destined for the practice squad... so why not waive him anyway, put him on the practice squad and go with Bledsoe, Travis, and Losman on the roster. This way, at least if Bledsoe or Brown went down, they could pull Zolman from the practice squad because no other team is going to sign him to their active roster.
So I say don't put JP on the IR...