Postfix/Postmap catch-all for local testing?

Hello all!

So this isn't exactly a Ruby on Rails issue, but it fits so well into
the RoR typical development cycle that I thought I'd post it here

I'm wondering if anyone knows how to configure postfix on a Mac so
that emails sent using the local SMTP service will _all_ be
intercepted and dropped into a local mailbox on the mac.

I found this blog post:
which has helped actionmailer testing ENORMOUSLY.

The problem is that what I really want to do is configure a virtual
alias that looks something like:

*@* username

So that any email to any address that hits the local postfix process
would be delivered to my local user account, which I can then pick up
locally for testing.

But I don't know how to do this and can't seem to find any
documentation on how one might attempt this. I know that one would
_never_ do this on a live server, but I'm only wanting to do this on
my Mac laptop so I can test RoR apps with existing user data and not
worry about it.

Thoughts? Anyone?


P.S. In the meantime, I have a development-environment-only hack to
change email addresses so that instead of "" they
end up as "someone@mybox.localhost" and then I set the postmap mapping
to be:
@mybox.localhost username
which works fine... except for needing the email conversion hack.