Update

Right, been working on this problem for about 6 hours now.....and I've gotten no-where.

I have proved several things to myself though:

Its impossible to remove a verts influence on a UV.
Its impossible for a blend-shapes UV's to effect the Primary model.
Projecting a texture onto the character mesh isn't going to work. (which throws doubt into animated textures for eyebrows)
Animating the UV's isn't going to work
Transferring UV attributes from an unmodified model isn't going to work

I'm really stumped by this and can't think or find any other leads as too what to do next.

1 hour later :OK there IS more thing to try that I've just thought of using blend colour nodes but if that doesn't work i really am stumped. Will try it in 'ze mornin