Dan
The problem with placing a rear-facing car seat in the front passenger seat is two fold (at least). The first problem is that most front passenger seats do not have the necessary attachment points for the car seats to secure them 100%. The other problem is if god-forbid the airbag does activate (remember it's not only the weight of the child but the car seat as well on that sensor, or even if it just activates) in an accident it thrusts against the car seat and can cause rather traumatic injuries including head, neck, and potential death basically from bouncing the seat back against the passenger seat at over 100mph (speed of airbag deployment)...I don't know about you but I'm not willing to risk any of those with my daughters.
I have two car seats in my Tahoe a forward facing seat behind the driver and a rear-facing in the center of the second row. My eldest in the fwd seat is pretty much self-sufficient but I can still access my youngest (4 months) in the center. Yes I have to turn around, but regardless of where they are placed when they start to fuss and require attention the safest thing to do is to pull over and attend to them...so it really doesn't matter where they are.
Like I said before, I know that placing a child in the front passenger seat is tempting for its convience but to tend to a fussing child is a distraction from the road which would place you at a greater risk for an accident (and airbag deployment) and the risk of injury to that child in the rear facing seat it dramatically increased (espically with airbag deployment).
On an aside personally I wouldn't want to go and tamper with a safey feature of any vehicle just incase it deactivates more than just what I think it will.