Yafray + Transparent Shadows?

Well, I have some plane with glass-alike material applied with single sunlight above. All I want - half-transparent shadow when light from sun goes trough half-transparent plane and casts it on a some random surface below. The thing is that in Blender Internal it works nicely casting half-transparent shade, calculated from opacity map (assigned on that glass material) but in Yafray all that I get - solid black shadow. All that I found after Googling - some suggestions putting photon light nearby. OK, I did that and I got some nice light caustics passing through glass BUT that solid black shadow still was there. How to get rid of it?
I want unblurred shadows casting from solid objects and half-transparent casting from glass objects, just like it works in Internal.
a) If I turn off shadow casting on that sunlight, I get no shadows everywhere and caustics from glass.
b) If I leave shadow casting on that sunlight, I get solid black shadows everywhere and caustics but thats’s not the result I would like to achieve.
What should I do?

Double up on your glass model. The one you want to see, have shadowless. Have the second, clone, glass model just for casting the shadow, but with otherwise invisible material.

Mmm. I can’t get half-transparent shadows in Yafray at all. I’ve searched a bit more and found, that this’s impossible. Looks like I’ll have to use composition tricks to achieve some nice shadows.