GI behind objects

[Shimakaze]

When working on my latest project I came across a problem I'd like some hints on.

When comping the animation I require one render of a foreground object as well as one of the background objects. By using "invisible to camera" in the object settings I can hide the foreground object to get a background pass, and I can mask out the background or use mattes to get the foreground pass. The problem I have is I would like to calculate the GI only once, and use it for both passes, as the GI calculation takes up most of the render time. (Irrmap+LC)
If I calculate the GI, and use the same irrmap file with the object removed I get artifacts behind it where the GI wasn't calculated. In a still image that could probably be fixed with incremental add, but that doesn't work for animations.
Is there a way to force VRay to calculate GI behind an object?
If not I would like to add a feature request. And in a similar vein, it would be nice if a render element, say VRayObjectSelect, could return the unoccluded object so it could all be done in a single pass with a hit to rendertime.

[Zdravko]

There is no universal solution here. There are some workflows which might work in some situation, but generally this will be hard to achieve that in one pass.
In some situation it might work using sphere fade feature in others it might work by taking advantage of the "Use irradiance map" option in the V-Ray materials.