I have actually done this........
We got a new windshield frame and replaced the damaged one welding in extra steel support.
Sawzalled the top off, right below the rear window lines, and removed all the window hardware from the liftgate.
Using 1.5" Steel Tube we built up a cage, basically very "YJ Family cage esk" but on a bigger scale.
Front hoop to help support the windshield, hoop behind the front seats, another behind the back seats and then tapered down to the floor.
Added in bracing and supports and tied it all into the frame with bushings.
turned out really well.