RMS groupings

Hey!
Is there a way to make groupings past units from different players?

For example, if I make a grouping with units from players 1 and 2, when I load that grouping, it pastes all the units as if they were from the same player. I don’t want that.
I have examined the groupings xml files, but there doesn’t seem to be a “player” attribute for each unit

Thanks!

Edit: just tested and adding player=“1” or player=“2” as attributes won’t work