Oh I see what you are saying. Here’s something to try:
WorldSettings->Lightmass->
DiffuseBoost 0
bUseAmbientOcclusion true
bGenerateAmbientOcclusionMaterialMask true
DirectIlluminationOcclusionFraction 0
IndirectIlluminationOcclusionFraction 0
Then use Stationary / Movable lights.
The DiffuseBoost 0 will remove indirect lighting from lightmaps - so they should be black. bGenerateAmbientOcclusionMaterialMask tells Lightmass you do want the AO accessible in materials. DirectIlluminationOcclusionFraction / IndirectIlluminationOcclusionFraction 0 says ‘dont apply the computed AO to lighting’
I haven’t tried this, but should do what you are describing, without messing with the settings that dynamic GI methods use (IndirectLightingScale on the light)