Never did it, but you likely need inserts rather than the wood screw type of mount. If it is epoxy based, you can epoxy inserts in. If it is a thermoplastic, you can drill it slightly undersize and use a big soldering iron to press the inserts in. Possibly, you could get a wood screw in that way, too.
Call Uncle Mike's or one of the other makers and ask for advice based on the make of the stock. Calling the stock maker wouldn't hurt, either.
Nick