XIF - Extracting Specific BP's to an external system from CRM

Hi,

We have a CRM system up and running along with a linked R/3 system and these 2 systems are exchanging Business partner data.

We now want to extract the business partner data to a third party system but a restricted list of Business Partners. I can see that I can add a new site and setup the BP's to go to another system, but I can not see how I can restrict the BP's to the external system but keep all of the Bp's going to the R/3 system.

Is this possible.