Grouping Meshes for Lightmass

We all know that Lightmass has problems when processing Static Meshes that should be connected which results in Light Seams.
I don’t know how exactly Lightmass is implemented, but aren’t the Lightseams caused by different Threads processing the Static Meshes?
However, sometimes it is not possible to to merge a mesh. In my example, my whole first floor uses the same Material and should not have any discontinuation through trims and such.

As you can see, the Floor is lit differently.

Now my Feature Request: What about an option to group Meshes/Actors Together so they get processed together in Lightmass?
I’m not talking about the Merge Actors option.

I think it’s something that should be an option unless they’re working on a different solution–while it will take longer to render, at least you could achieve the quality that you want.