Select Source Subinventory in RSSP

Using RSSP, we're looking for ideas on how to still be able to split Picks for IMT/Transfer Orders based on Source Subinventory within the same Inventory Org. We have an Inventory Organization with two Store Room/Subinventories, one for each hospital they reside in. In Classic SSP, you could select the Source Subinventory, which you could then define in the Pick Wave Release Rules to select by. - In RSSP, you cannot select the Source Subinventory in the req, so the Transfer Order cannot populate the Source Subinventory.

This is a dealbreaker for us because it completely negates the ability to allow the departments to order from the on-site subinventory.