[Exim] %1@domain.com forwarding

Major problem and I can't see an answer in the docs or faq's sorry!

Just upgraded 6500 email accounts from sendmail to exim and discovered (too
late) that exim doesn't have quite the same feature as sendmail.
In the sendmail virtusertable we would have @domain %1@someotherdomain

ie mail to bob@domain would be passed on to bob@someotherdomain
tom to tom etc.

Can't see how to recreate this in exim, any pointers?

Thanks for a perfect mail system!! (Even if it doesn't do %1 out of the box
:-) )

John