I think that would work. If my research is correct the WetFire is powdered magnesium trapped in a cube of thermosetting plastic. Be warned that when you do open the original packaging and start breaking the tinder into smaller chunks whatever magnesium is exposed to the air will quickly be rendered inert. I think you are better off coating the intact cubes with wax rather than breaking them apart.

Also, I would use a fairly flexible wax like the stuff used to coat cheese rather than brittler waxes.

-Blast