Obviously not a common problem, but as I sorted it figured I'd post my solution in case it helps others.
As previously noted no heat based tricks worked.
Ended up taking a small phillips head screwdriver and poking a hole into the foam in the center of the divot, then worked radially around the dent, about 30 degree increments, marking the location/direction with a pen, and gently lifted the foam, creating some gaps between the core and foam. Injected some silicone into the hole, pushing the nozzle well into the "slots" and working it into the cavities I made with the screwdriver. Slightly overfilled the core, bulging it a bit, then worked the foam back to the desired shape, squeezing out excess silicone back through the entry.
Let set.
Then used some batting I had, about 1" thick but compresses to 1/16" between your fingers and cut a piece that fit over the foam, inverted U lapping over the ends by about 1-2" and even with the bottom edge front and rear. Worked the new upholstery on and it looks pretty good IMHO.
HTH someone...
