My wife has a new X5 to hall the kids around, but I did put a rear-facing child seat (11 month old) in the back of my BRZ for one trip and it compromised the front passenger seat and getting him in and out was like reenacting his birth.
SO baby seats and rear facing seats wouldn't be practical, but once they're old enough for front facing you could be in business.
We're getting two of these seats to take on airplanes, and they're so small that I think they would be perfect for the BRZ:
http://www.albeebaby.com/diono-radia...hadow-old.html