RGB alpha

[Ekenryd]

When using the mtl wrapper to catch shadows and GI I get a very nice looking alpha channel with colored GI/shadows, but how do I use that in post? As it is in the alpha channel, it all turns to white when I batch render, so I loose all the colored GI info. How come the vfb have a rgb alpha channel?

edit: oh, found the solution the moment after I posted this. "Output alpha as seperate file" in render settings. Though maybe it would be nice to have this as a render element instead.