Your request concerning having a modeled sky dome with a separate GI sky light source has been an issue that I've wanted forever.  My interest has always been a little different.

I would like to have a background/atmosphere that would provide light for the GI and a background/atmosphere that would be rendered into the image.  For me, this has been useful for space scenes.

I would like to use StarBright for the star backdrop but I would like to use a b-gradient for the lighting.  At best, I have to do two renders and combine them for animations.  I can use a backdrop for single scene renders but it's only for single images.

-Kix