In Logic, track and channelstrip are different/disctinct objects/entities, which become linked when one is assigned to the other.
AFAIK, the group feature pertain to the channelstrip domain (which pertain to the mixer).
Hence, I might be wrong but I don't think there is a way (yet) to proceed without going into the mixer...
I see.
Is there a good place to read about this difference between tracks and channel strips? I don't recall that being specified in the manual, but perhaps I missed it.