it can be done
yes you can do it, but you will have to be very patient. in this case the molds are more likely to crack than the glass, so you will have to start on very low wattage and increase very slowly. I never could muster enough patience myself when I tried it in a microwave kiln, but I have a friend who makes gorgeous cabs in her microwave kiln in such molds.
it might also be a good idea to elevate the mold a little with something, maybe thick fibre paper strips or something.
hotline primo primer is a very good option for priming the molds.
good luck !