I'm sorry to say that a wheelchair will not fit upfront as everyone has said.
If your DH can transfer including a step up into the cab and then a step down at the end, it could work. Our daughter has ridden up fron a few times but we've carried her on when she was little or supported her as she grew. Then one of us (actually me because I volunteer) goes into a regular cabin with the chair.
The seats are narrow and angled though so he would also need ample trunk stability (Sue, help me with the right terms, please) as there is nothing to hold onto either.