Pachmayr makes and sells a variety of 1/16" thick closed cell foam sheets. Pac-Skin I think it's called.
Just cut out a piece, de-grease where it's going with alcohol, peel off backing, and slap 'er on.
Will give you a little more time before it gets too hot, and is particularly useful when the stock is ice-cold.
Should it show signs of de-sticking, it can be affixed with small self-tapping screws (with washers) around the perimeter. You will need to pre-drill holes for the screws, and be certain that the screw shaft does not extend into the interior of the receiver and interfere with the mechanism.  

Send it to Kurt, who will mill some cooling holes along the side.  Take a look at some of the mod's he's made.  If I had an M17, it would go straight to him before I even bothered to shoot it.

www.kurtskustomfirearms.citymax.com/page/page/42606.htm

-Troy