if you could select the toe cap as a body part to make it invisible, it would have to be a whole different body part rigged to follow the toes.  i'm not sure you'd save any resources like that.

if you're just concerned with using stocking MAT poses, you can just apply a MAT pose to make stockings work. on any figure with UV mapping. because the creator of the MAT pose can define what it does, including referencing scripts and using masks and working with the .  but if you're talking about making MAT poses yourself, and on most figures, there's a material zone for the legs that sort of suffices. that's what Bluebeard used to do, as far as i can tell.  personally, i feel the masking method not only gives you the control you need, it gives allows the artist to have the skin under the stockings match the skin everywhere else.  that said, i have no clue how to create a script like that, or call it from a material.  i just know people have.