alpha-channel in gl.videoplane?

Hi,

can someone tell me how to use the alphachannel of an (still)image in a gl.videoplane? I dont want to mix it with another image in the same plane, but just cut out the image with its own alpha so i can see other things of my render context beneath. (I hope I explained myself alright).
Probably there is a simple solution, but i just cant find it. If I use for example a jit.gl.slab with co.alphaclue.jxs and send the same image in both inputs, it works. But I cant imagine, that their isn't an easier way, is there?

Thanx a lot,
Rene