I would think you could rejoin the teams, then re-split the support team which would have one fewer men. Doesn't it currently work that way with AT teams split from squads?
Also, we are talking about ammo sharing, but I think the sharing is only for crew served weapons, such as MGs, and RPGs/rocket rounds. I don't believe Steve said or implied that rifle ammo will be shared. Steve, please clarify, or do somefink.