I did similar for a La Femme freebie a few years back.

It requires a manifold mesh to do properly. I can't recall if M4's eyesockets are manifold ( "watertight" enclosures), I know the millenium figs mouth interiors are not manifold. I'll take a look at M4 after work this evening, if the sockets are enclosed I'll wip up a quick injection file for you and post it here. This sort of thing is easy to do with the smooth and flatten brush in an external sculpting software. Or you, or someone else, could take a crack at it. I'll check back tonight, if no one has shared a solution I'll make it for you if you want.