Remove the recoil pad, fill an old sock with lead shot or sand, stuff it in and install the pad. I thought about adding weight for my 300 WinMag barrel, but the with the t-hole stock recoil isn't had at all, the stock design is a good one. I poured 4½lbs of #9 shot into the t-hole Flex-tech stock for bench work with my 375H&H TC Prohunter barrel, that would work too.
Tim