[Exim] vacation problem with virtual domains (local domains)

Hello,
I want to have vacation message for mailboxes who are not in my domain, but virtual one.
for example my domain is foobar.com, but i have also disaster.net & other.
can You help me please to find a working solution for this ???
I don't wanna have shell users for this mailboxes

thanks in advance
Todor Popov