[Exim] Aliases file and parked domains.

I have a virtual host with one main account, and two parked domains
underneath it. I want to set it up so that someuser@??? will also
receive mail addresses to someuser@??? or
someuser@??? .
Currently I am using exim version 3 along with cPanel, i have an aliases
file for each of the parked domain, and I can make the above scenario work
by putting an appropriate alias into each file, this is a bit cumbersome.

Is there an easier way to do this, someone mentioned that I could use an
alias like *@firstparkeddomain.com =>%@maindomain.com, but I cant get this
to work?

Am I barking up the wrong tree or what

tia
garry