Just heat some rocks in the fire - transfer the rocks to one side; cover the rocks with a layer of wet vegetation such as Sphagnum moss; place the boil in the bag on the first layer of Sphagnum moss then cover the boil in the bag with some more Sphagnum moss and then cover with sand to hold in the heat; wait 10-15min to steam heat and then tuck in.

Similar idea to Ray Mears cooking venison on the West coast of Scotland

http://uk.youtube.com/watch?v=ayKMitUKz-g