Welcome to the forum man. I'm sure you'll find all sorts of help with the design and layout of your room.
First thing, you are talking about surrounds (5.1) not rear surrounds (6.1, 7.1,etc.) If your room allows it these would probably be best placed to the side of the main listening area, above the listeners heads about 2-3 feet, and slightly behind them.
Depending on your receiver you should have no problem installing that one surround on the wall further away. Your receiver can compensate for the extra distance, when you enter in the distance from your listening area to that speaker, during your setup. Plus, you'll adjust that speaker's audio level, with your analog Radio Shack SPL meter (you do have one don't you?)
Why don't you post us back with the gear you are running/installing? It'll help folks give you some additional feedback.