Package .Runtime directory

I noticed a .Runtime directory in packages like Burst and from what it looks like it is used to get around conflicting with dependencies from other packages?

I would like to do the same. I have a couple of System.* dependencies that I'd like to bring in certain versions but when I place them in the .Runtime directory they don't seem to get picked up.

Any idea how to make them work? Do I have to load those assemblies manually?