Dynamic DNS hostname as source address?

[digilink]

I have a friend with a dynamic dns hostname that I want to use as the source address for a firewall rule to allow him SSH access to a box on my LAN. While I could easily enter his current IP address, and it would most likely remain unchanged, I'd prefer to enter his dynamic dns hostname instead.

Is it possible to do this, and how would I implement it? I looked at aliases but it's still looking for an IP address…

[jimp]

If you're on 2.0, make an alias, put the hostname in the alias, and then use the alias in the firewall rule(s).