DepthMask with alpha

Hi,

I've been searching, maybe it's been answered but couldn't find it. I'm using the depthMask shader on a plane and works fine, but i'd like to mask only parts of a plane through an alpha (the 'hole' is quite a complex shape). Is there a shader available out there, or is it even possible? Or am i stuck with constructing the mask with geometry? (I hope i make sense ;)).

m