Hi Nick,
You could probably contact;
licensing@cisco.com
to have these (DLU) licenses re-hosted to reflect the mac address
of the Publisher (first-node) server at the other 6.x site. Keep in mind
that 20 DLU's that these licenses cover will only get you 4-5 phones
installed (depending on model). So it may be a fair amount of pain for a small gain
Cheers!
Rob