[libvirt] sending openvswitch "port db" info during libvirt migration

Someone asked on IRC the other day about sending openvswitch per-port data (normally stored in the switch) to the destination host during a migration. I suggested maybe this could be handled by encoding the information into the interface's <virtualport> prior to migration, and then writing it back out to openvswitch on the destination when the interface was reconnected there. I think there's a problem with that, though - they don't want to save the port data on the source until the instant that the interface is disconnected (since it is constantly changing), but by then the domain XML has already long ago been formatted and sent to the destination. So is there some other way within the confines of the current migration protocol that this information can be sent from migration source to destination?