cut the riser block in half from back to belly, glue a 1/8 - 1/2" thick piece of something in the middle. I've been using g10 as it makes me feel better about the strength with the riser design i use. Phenolic and hardwoods are common as well. I think if you look at Kenny's last two builds, you can get a pretty solid idea of it. He has been doing his risers as mostly pheno with thinner wood sections on the outside, they look pretty amazing and are probably super strong.