Set Exchange 2010 account defaults?

I'm setting up my first Exchange server, which will import ~150 mailboxes from an offsite IMAP server.  Obviously, I'd like to create these accounts en masse, but the creation process isn't straightforward as it seems.

I can select multiple accounts via Exchange Management Tools, and create all of them simultaneously, however, they all create address resembling firstnamelastname@domain.local.

They need to be firstinitiallastname@outside.org

For example, John smith appears as johnsmith@domain.local - I need jsmith@outside.org

Hopefully this doesn't require too much scripting?