My understanding is that dvmhost can currently have a "global" LLA key in its configuration, which means every subscriber accessing that site must have the same key loaded.
This presents the obvious issue of having to share LLA keys between multiple subscribers, but also means that all of the sites a particular subscriber unit affiliates with must have the same LLA key configured.
One way to implement this might be to add a field to the rid_acl.dat with that RID's LLA key in it.