There is a lot of flexibilty, production time-savings, and specific look development which can be gained by building lightmaps (for realtime engines) in passes. Using mental ray, these passes are fairly easy to setup and bake. However, while final gathering (FG) works great (result-wise) for radiosity sampling, it is only single threaded when used for rendermapping. Seeing as how FG is a screen space method for sampling, I don't know if this can be called a bug (definitely an oversight). This limitation is made worse when several computers are used via satellite rendering to generate a single lightmap (or lightmap pass). The other systems sit idle, while one machine (using one core) calculates the FG prepass.
To avoid this production slow down and get your systems rendering with full CPU power, an environment sampling shader can do the work FG would normally calculate. Using mental ray's ambient occlusion shader with the below parameters, I generated the environment sampling with satellite rendering using 100% of 24 cores.
pass material setup
environment sampling pass: using the occlusion shader for ambient lightmaps
Use this sampling method with interactive IBL light domes
for a fast and iterative lighting solution.