Textured transparency shadows - is there an easier way than this?

Okay, due to Project Blazing Monkey, I am testing some features in Blender. As I found no built-in function for making textured transparencies cast equally textured shadows (all shadows, even with raytracing, is just as if the casting object is opaque), I built a method myself; the results are below.

My question is: Am I overlooking this function (textured alpha/transparency shadows) somewhere, is there a simpler way of doing it, or will I be needing to use this method for future cases as well? I have a lot of alpha uses, and objects casting solid shadows is Not Good.

My example:
(sorry about the size)

As you can see, this (completely arbitrary) setup just has 3 planes, the top one (red) with a ‘blend’ texture on the alpha. That has to cast a comparative ‘blend’ shadow, rather than the usual solid one, on the object that the red plane is blocking light from. This method (a shadow mask for textures captured by a secondary camera alligned to the light source, then projected as negative light by a similarly alligned second ‘light’ source) should be usable for all my needs, but it takes too much time to set up right, and is in general a pain. Is there something simpler with this kind of result?

PS: I prefer something that, like the above pic, is reproducable with just buffer shadows, but if raytracing is the only way, I am still interested in how.

click Ztransp. I think Blender should have this enabled by default.

For best results I’d use raytraced transparency and set the TraShadow button for the objects RECIEVING the shadow. For a more colored effect you can crank up the filter variable.

I thought it would be default, too, but it isnt (as far as I can see). But the Track Shadow worked, thx!