A typical recrystallising technique is to dissolve MDMA.HCL in 3.5 times the amount of boiling IPA, add 3-4 times that amount of acetone and let sit in the fridge overnight, next day filter out about 80% of the starting salt. Then boil most of solvents away, add a bit of fresh acetone, cool and collect another crop of recrystallised MDMA.HCL.
So with this in mind, I'd try this experiment. Weigh say 1 kilo IPA, gas it like mad and weigh it again to work out the HCL loading.
Then assuming it's say 7%-10% HCL, I'd then add 250g-300g distilled MDMA freebase to this HCL/IPA mixture, shake, maybe add some acetone to help crash out the salt and let sit in the fridge overnight thereby combining the gassing and recrystallising into one procedure. But, if the HCL loading is low this won't work.
Maybe some bees could shed some light on how much HCL IPA can absord.
Abacus