relaying mail

[Michael Grant]

In one of my domains, I have the MX record for it set up to my server.
 But for one of the users within that domain, their mail needs to be
shuffled off to a different server at google.  But I can't just
forward it because it's like an MX host I'd need to forward it to.
And I can't alter the MX to point to google for the entire domain
because it's only one user within that domain, the other users will be
screwed in that case.

For example, mydomain.com, let's say the mx for that comes to my box.
For joe at mydomain.com, I need to send his mail to ASPMX.L.GOOGLE.COM as
if it were the MX for mydomain.com.

In the old days, one would simply forward email to
joe%mydomain.com at ASPMX.L.GOOGLE.COM.  That would cause mydomain.com's
sendmail to connect to ASPMX.L.GOOGLE.COM and shove down a message for
joe at mydomain.com.  But that seems long deprecated because it didn't
seem to work.

I am using sendmail and procmail.  Can anyone think of some way I can
cause something like this to happen for just one user, ideally in a
.procmailrc file?

Michael Grant