A work around, though it's not a true Private call (meaning it won't alert a radio) is....any DMR ID can be used as a talkgroup. So I would use my DMR ID and set the DV Switch Bridge up to connect to that ID as a group call. That way I can use the Shortcuts app in iOS to trigger a connection on the ASL side to an ASL node and use that "Private" Talkgroup via a hotspot to go out on the ASL connection.

Others can use that "Private" talkgroup if they know the number, but it gives you a small way to do this. 

Not sure if that helps but maybe a thought?