Bolts,
Just my opinion, but I think the S1 and XL1 have much different swing weights, and I don't think the 2013 XL1 feels any less end-loaded than the 2012. Most of the stores around here will at least let you swing the bat, even if you have to step into a back room for safety. That might be enough for your son to judge.
Please tell me he didn't break a 2013 S1 already!