Has Marrone said anything about playing time allotments for Leinart and Tuel?
Not that this would happen (it sounds stupid), but I'd put in Leinart for a few series, and if he sucks, get Tuel in there as soon as possible to get as much experience as he can before Week 1. But, if Leinart's doing well, keep him in longer and start him Week 1. So.... name the Week 1 start on the fly Thursday night and get the man some reps.