A single speaker directly behind your head will often cause the illusion of the sound coming from in front of you. So in that case it's better to not have the rear center, as it creates a completely wrong sound field.

If you don't sit directly in front of it, but instead have two seats to either side, then the rear center can provide a more connected surround effect.

It's hard to say how well it will work. As long as it's not too much effort, you should probably just try it, and see how you like it.
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Pioneer VSX-1018AH-K, PDP-5020FD, DV-79AVi
Axiom M22s, VP150, QS8s
Sony PS3, surround backs
-Chris