We had a crayon mishap over Christmas break. Probably the same kind of problem - waxy build-up. I had looked online and saw recommendations for Oxy Clean. I used the spray-on kind in combination with Borax, white vinegar, and some Goo Gone.
I don't know what worked, but the orange crayon came out of everything. I'd recommend doing a google search to see if anyone's had a similar experience with ChapStick as the petroleum products are slightly different.
Now, I'm trying to figure out how to get dry erase marker out of a new pair of our daughter's pants. They were $4 at Target, I'm probably going to spend more money trying to save them than just replacing them.
Good luck!