hmm, i dunno thats a toughie.

i would suggest boiling it though. I took my pipe and put it in a large glass cup filled with water, put the cup inside a pot of water and the pot on the burner. This is all after i scraped it with a paperclip to the best of my ability. When you boil it, the resin that wasnt easily scraped should be very easy to get off.

This is all assuming you have some time to boil it with nobody around to smell your kitchen.