Jaso has a "Paint and Epoxy Remover" that turns epoxy back into goo. Then you have to mechanically scrape the epoxy residue off, repeat many times and finally acetone the daylights out of the wood to get it re-epoxyable. It's usually easier to grind and saw that go this route. Nasty stuff to use, too.

http://www.homaxproducts.com/product.../10/index.html