I use it for primer instead of mixing my own colors, but that is just me, however I wouldnt put it on your eyelids just because of the way it drys it would probably crack and what not because of all the movement and blinking you do.
What do you use the Lash-Mixing-Medium for anyway? To turn piggies into Mascara? sorry it doesn't really belong to this topic but I'm just too curious...