AvaStar users have Gaia Clary’s survival kit for Fitted Mesh. Now Astrid Kaufmat has put a survival kit for Maya users up in the SL Forum. See: Maya Survival Kit (for fitted mesh).
Neither Gaia not Astrid are claiming these kits are the end-all-be-all solution for working with Fitted Mesh. But, they will help you survive the current state of affairs.
Astrid recommends getting the plugin ngskintools, which you can download from here. She links to guides and tutorials for using the plugin in her post, link at top.
Astrid’s basic work flow is to weight to the mBones as Maya users have prior to Fitted Mesh. Then copy the weights to the collision bones we have now. She uses a script named abweightlift, which can be downloaded from the creativecrash site. Her post explains how to use it.
I don’t use Maya, so I can’t say this is good or bad or even easy. But, in Blender I know getting weights from mBones to collision bones is a common task. So, having that ability in Maya seems to me to be a necessary step.
I believe the process of moving our weights from mBones to collision bones is not going to work that well. It works. But, the shape sliders aren’t working as well with these meshes as I expect they can.
I think a blend of weights is needed. Replacing the existing weights on collision bones with the mBones weights is going to throw off the shape adjustments. At least that is my thinking for now. But, I have a lot to learn about this and many things to try before I know.
Try out Astrid’s suggestions. Provide feedback in the forum after you’ve tried her process and express thanks for her taking the time to put the post up.