IK Script and Optimized Avatars

Does anyone know a way to influence the joints of an optimized generic mecanim character?

I have a generic Animation Type character that needs ik controls for a couple of its arms. If I expose transforms for the arms and attach an IK script, the lines that indicate the asset's function look correct, and if I select the transforms of the bones, they seem correct, but the character's skin doesn't deform to match. It appears that expose transforms are merely for attaching to, not actually manipulating the skin. Is that true, or is there some trick to make the skin deform withe these exposed transform?