Pan, although they're side surrounds(if you're talking about a 5.1, rather than 7.1 setup), they don't necessarily have to be placed on the side walls. A good spot for the side surrounds in a 5.1 setup is on the side walls about 2' farther back than the listening position(to give a little back surround effect in the absence of back speakers). If you mean than you'd be sitting about 2-3' from the back wall, then putting them on the back wall and widely separated almost to the side wall position would work well. If you're going to be sitting a lot farther than that from the back wall it'd be better to put one on the side wall, back about 2', and the other possibly mounted on the ceiling above where a side wall would have been(or possibly placed on a stand).
