After a few months of not being able to sit and play around, I'm finally working on a new character rig. The character has three long hairs sticking out of his chin that I'd love to have wiggle around as he talks:

My idea was to have the mouth driven by two smart bones (one to control the width of the mouth, one to control it opening and closing, both pointing at a target bone, as in the image below)

I have the ball of the chin bound to the main chin bone (the blue one pointing left) and each of the three hairs bound to individual dynamic bones, which are children of the main chin bone. Moving the target for the mouth control moves the ball of the chin around, and everything moves -- but the dynamics of the chin hair bones aren't working. I'm assuming this is just because the position changes of the chin bone from the smart action aren't being translated to the child bones -- when I manually animate the chin bone, the dynamic children work as intended.
Is there a better way to approach this effect? I'm not tied to using a mouth control with this setup -- this was just the only way I could think to get those chin hair bones moving dynamically with his lip flap, so if there's a better overall way of doing it I'm interested in hearing it!