[Exim] Sendmail-like virtual domain routing with Exim 3.xx

I'm trying to set up Exim 3.35 to behave like Sendmail with the virtuser
feature enabled. Basicly, I want a fully-qualified aliasing system, where it
matches the full address and specifies the mailbox to deliver it to. For
example:

john@??? -> jsmith
john@??? -> jjones
john@??? -> jwaters

Does someone have a (relatively) simple example to make this happen?