The 2WD version of the Commander has a transmission with a different tail section casted into the case of the transmission. Because the end of the transmissions are different between 2WD and 4WD, because one has a XFR case bolt to it and the other has the driveshaft bolted directly to it. Think about it, that also means the 2WD versions driveshaft to the rear is longer to make up for the difference of the XFR case NOT being there.
Usually folks ask this question in reverse, Can I convert a 2WD version of a vehicle to 4WD, and the answer always turns out; you need to replace the entire drivetrain of the vehicle, the final cost will be more than what a used vehicle is worth.
Unfortunately the same is true for you; converting your 4WD to the 2WD version will require an entire replacement of the drivetrain minus the engine and rear axle. More than the cost to fix the Front drivetrain problems.
Can you disconnect the Front Drivetrain and just use the Rear Drivetrain to make it 2WD? Not without a lot of risky, expensive and unreliable modification. It also depends on the 4WD system you have.
The QTI has the simple NV140 XFR case, it has an open differential that will NOT transmit power if the front drive take-off is free-wheeling with no resistance. The vehicle likely will just sit and spin the take-off for the missing front driveshaft. (You'd have to take the XFR case apart and do some major modifications that likely will be unreliable and ultimately fail sometime down the road)
The QTII and QDII have a clutch pack inside them, "MAYBE" you could somehow trick the XFR case to engage the clutch pack and defeat the differential in the XFR case, and thus you'd be able to drive with the front driveshaft disconnected. (The clutch pack only engages normally when you are in 4WD LOW, which isn't practical for day to day driving). But, the clutch pack is designed for a much lower load of just locking two closely matched front/rear loads, NOT to transmit all the power to just one side. My guess, it would be likely to slip and burn up, leaving you stuck on the road and needing a new XFR case sometime down the road.
If you want the vehicle to drive normally and reliably, likely your cheapest option is to just repair the broken components and keep it in the configuration it is now.
***Yes, Jeep Wranglers you could do this easily, they have a totally different 4WD system than the Commander. They normally drive around in RWD only, cause the XFR case is designed to do that. Wranglers also can NOT be shifted into 4WD unless you're on a soft surface that allows the wheels to slip, while Commanders maintain 4WD for all conditions all the time.