Well, I'm going to find out. I scored a 6-disc head unit from a 2011 RAV4 with built-in XM tuner on Ebay. I couldn't believe that nobody else bid on it:
Toyota Rav4 06 07 08 09 10 11 OEM 6 Disc CD Radio w/ XM Satellite radio | eBay
For $49 + $16 shipping I just couldn't pass it up. I'm going to try to swap out my 2008 head unit for this one and see what happens.
All I need is the XM antenna and a place to mount it. The seller says he's including that square blue antenna plug. Does anyone have any suggestions on an antenna and where to mount it?