Groupwise Mailboxes

Our previous Net Admin setup our company (150 employees) into 3 SEPARATE TREES. I am working to combine the company into one tree. The problem is he duplicated userid’s into the main tree (Corporate) to be used as their Groupwise mail ID’s. I will be making the perpherial trees into OU under the main Organization. What I need to do is relate their ID in the new OUs to their existing Groupwise Account, so that they don’t lose their existing mail. Is it possible to do this? Does anyone havesimiliar experience? PLEASE HELP!!!!!