Removing the outer skin by the methods you suggest would likely be the best approach. Either way, the metal will need to be dressed up quite a bit, as bending the rim open and then bumping it back shut would likely result in it not going back exactly like it was, and may actually crack the rim. I kind of like just grinding off the rim to free the cover then carefully welding the two pieces back together.
Another approach might be to cut out the center of the liner, leaving the rim intact, do your dent repair and welding the liner back in or even leaving it out completely. There's no telling what you're going to find between the layers, and if you're worried about structural integrity and/or warping from welding, you could clean between the two parts and use JB weld to stick the them back together.
I haven't tried the stud welder approach yet, but that may be the least destructive approach. I plan on using it on a few dents on my cab where the back side is not accessible.
