If the mail server has rimapd set up (imap-uw can handle this, but
I don't think pkgsrc does it by default), you can use ssh (or rsh!)
quite easily.  I've got in my .fetchmailrc

	poll <mailhost> proto IMAP
		plugin sshmail
		password "none"

and sshmail is:

	#!/bin/sh
	exec ssh $1 rimapd

I've got rimapd in my path on the mailhost - you may need to use
/etc/rimapd or some other pathname.  This way you don't need to
play around with port-forwarding, etc.

Simon.