anything is probably possible if you want to through enough money at it, but i would guess that all the off the shelf, after market power roof fitaments for the Element would be too small to replace the huge opening in the stock rear roof. you would also have the issue of where the glass panel would slide. it would likely have to slide inside the roof toward the front and that might be a challenge. i think that it couldn't slide outside the roof toward the rear because the factory opening is too far back on the vehicle. the only other option would be that it slide outside the vehicle toward the front, which is the exact opposite direction of how all of them are designed to operate.
the prognosis is slim to none unless you have unlimited capital to spend.