I've been wanting to try this for some time now. So, I stopped in at the Dollar Tree last night and picked up some cute silicone ice cube trays. Went though the crayon bin at home, grabbed all the broken ones. Took all the wrappers off and put them in the trays, and melted them in a preheated oven at 250 degrees.
When they were all melted, I carefully took them out of the oven and stuck them in the freezer to set. After that, they were easy to pop on out and use.
P.S. muffins tins work too!