Citrix Farms and Licences

I have a customer with two locations with seperate AD domains and forests, with a 2 2MB MPLS link between the two.
The main forest and AD domain has 7 servers with Citrix 4.5 presentation.
In rolling out an SQL ERP application, we plan to have the live ERP server in the main forest and an identical DR server we need to replicate the SQL data on to it using DoubleTake.
How do I establish a trusted connection between the 2 AD Domains which allows us to see the Citrix License server in the main AD domain so we do not need to purchase additional liceses for the secondary Citrix farm where the DR server is located.Advice would be much appreciated