I have used Devcon Epoxy Putty before on a Hogue aluminum bedded, rubber overmold stock...
ITW Devcon | Magic Bond
I was only aiming to fill the gaps slightly between the full length aluminum bedding block and the receiver just around the recoil lug area. I used Johnson floor wax as the release agent.
I was worried about it being too brittle. But, it seems to be holding up just fine although, I haven't taken the stock off in several years.
...but, perhaps you're talking about a plastic stock chassis?