Variants in a multi-board project?

[g00se]

I can't seem to find anything in the docs regarding the use of variants in a multi-board project...   I am using Altium 20.

I am trying to specify a variant for one of my child projects to be used in the multi-board assembly and in the multi-board ActiveBOM, but I don't see any way to specify a variant.

Has anyone done this?

THX