i'd take the racks out and run it empty, as soon as the element starts to heat up, see if you can loosen it. You might have to open it several times during the cycle to know when it will let go. If its hot enough to melt it on to it , it should reach a temp that it will let go before its too hot.
Thanks for the advice; I ended up doing what I was afraid I would have to do in the beginning ... the back and knee breaking job of picking and scraping the plastic residue off by hand. Between a screwdriver and nut pick the element is as clean as ever! What miniscule amount that is left I can wipe off when the element heats up again as you both suggested.