When has he said he'd sign THIS? He did say he'd sign a simple renewal, but I don't recall him ever saying he'd support any expansion.
I don't know if he said that or not, but he has stated that he will "sign whatever Congress sends him" in regards to numerous bills. I just don't know if one of those "numerous bills" had anything to do with the AWB.
Like it matters though, since he hasn't vetoed anything yet, and he's had some pretty bad bills reach his desk.