limit the LOV in vacation delegation to active employees.

Hello

Managers are able to select  external users (irecruitment users) in vacation delegation. We need to limit the LOV in delegate option to active employees only. How do we do this? e have an instance where few managers mistakenly selected an external user who had the same name as employee but different recipient role (john.doe@outloo.com) . The workflow notifications for all itme types have gone to this external user which is a security issue. Please let me know how to limit the LOV in vacation delegtion to only active employees.

Thanks

srimathi