I wish I could help, but I've decided that unless I am using a full-length body pose and exposing all the shells at once, I just use the one that is the current focus. Another option I have used is Photoshop on extremely high res and zoom. There I use the healing fix to take a texture that is the right color and add change the color post rendering.
Trust me, I realize the trouble that seems to be, but once you zoom out, you never see the fix. Static poses are easy, but I get if you have a sequence of more than a few it's very tedious. What matters to me is the realism of the end product. Sometimes I just have to pose the character or use the camera to move past the issue.
I'm sure you've thought of or done something similar. I just wanted to let you know you're not alone in this regard. The one that bugs me most is using some of the tools for wet effects when showing the entire model in a swimsuit or a nude and the problem peeks through. So I hear ya. I'm gonna try a few of the above solutions as well in the future.