Here's what Dolby recommends:
http://www.dolby.com/ht/Guide.HomeTheater.0110.html#s3.2
As I understand it, the general consensus seems to be slightly behind the listening position, and 2 to 4 feet above the listeners ears. But, I've also heard that if you can't get the surrounds behind the listening position, then slightly in front of it will suffice. Can't speak from experience though.
If you put yours on the side walls, say a foot behind the listening position, that would leave you two feet from that back wall, and I would think that would be OK. The above link will provide you with alternative positioning. It recommends experimenting, but in your case, that would be difficult because you (wisely) want to run your wires BEFORE drywalling.
