[Exim] Domain Forwarding

OK - here's what I want to do.

I want all email coming in for *@muttcats.com to go to
*@lexiemorgan.com.
Maybe do this with a file called domaimaliases that contains

muttcats.com : lexiemorgan.com
coup2k.net : coup2k.com
coup2k.org : coup2k.com

Then - I want to do some fancy aliasing.

I have an alias file aliases.yronwode.com which contains aliases for
that domain. But - if the alais isn't found I want to redirect the
remaining email to the same user at luckymojo.com. Thus cat@???
-> cat@??? only if there isn't an alias in
aliases.yronwode.com.

What I'd really like to do - if it worked id to have an entry in
aliases.yronwode.com as follows:

*.yronwode.com: *.luckymojo.com

Any ideas on this?