So did you make any head way on this yet? I am just starting to through aroung the idea  of a dedicated driving cab. I too am looking at doing something to accomidate 2 players. 
I am still in the search phase and your post is one of the ones that came up. When dealing with a dedicated driving cab alot of questions need to be answered for me. Including but not limited to which platform to use (PC, xbox, ps2, dreamast) the best controls to use. 
I am assuming there will be some more info that i find just wondered what progress you have made.