They would actually be referred as left/right surrounds, not rear. You would normally want to place them to the left/right of the listening area. Rears are introduced in a 7.1 setup.
Also, I assume you don't want to use a sub, or you would have 4.1.
To answer your question, sure. Since you would not have a front center channel, your left/right mains can be run in phantom mode on most AVR's to simulate the center channel. Most of the dialog (voices) from movies is in the center speaker, it is very important for movies. Since you don't have a sub, make sure you pick 60's or 80's for good bass, however, it won't give you the same experience of LFE that a sub can give you...
