I have done this using a turkey cooker. First I will cut off as much of everything as I can from the skull. Second I will suspend the skull in the pot full of water so that only the skull in under. Then boil for a couple of hours adding water as needed. After boiling everything else pretty much falls off. After you get it cleaned the way you want it I will put 1 part bleach to about 4 parts water back in the pot. Making absolutly sure to only get the skull wet I will put it back in the solution. I pack cotton balls around the skull at the antlers so the bleach gets to all the skull but not the antler. Only leave in the solution for about 15 minutes then check. If you need more time you can always put it back.

Hope this helps. It has worked for me a couple of times. Good luck with it.