mask one gameObject mesh by another mesh vertex transparency

in flash there is very simple possibility to mask one movieClip by another with trasparency

while in unity you can mask by depth mask http://wiki.unity3d.com/index.php?title=DepthMask

or stencil buffer without transparency

or you can mask by shaders, but we need animation in the masker

also i know about masking by texture rendered by camera, but that's too heavy for mobiles

is there any way to acomplish masking of one quad (or sprite or whatever else you can put texture on) by generated mesh based on transparency of vertices on the masker mesh?

edit: no answer? is nobody interested in 2d masking by dynamic mask with transparency? or it isn't possible? still nobody? (sry for updating this question but i believe it's feature every 2d-game developer needs)