matte shadows included in alpha

[highpoly]

I am trying to get matte shadows (from just my GI, no direct lights in scene)
to show up in my alpha, but not the object the matte assinged to. I right clicked the object and picked 'matte' and 'shadows'. I played around with the alpha contribution spinner and either get the entire alpha of the object included (1) or no object AND no GI shadow (-1). I just want the GI shadow to be in my alpha..any ideas??
thanks

[Da_elf]

you turned on the shadow option i take it?

[highpoly]

yep. I think I got it, I noticed if I turn the alpha contribution to -1, i get
just the GI shadows, which is what I wanted....strike one up for playing around with spinners! if this is not the correct way, please post..thanks