[rt-users] getting username from userid in a template

[Mark]

I created a scrip to run on owner change to notify admincc's via
template "owner change".

In the template I have:

Subject: Ticket Assigned to: {$Ticket->Owner}

This will print the new owner's userid, but I would like to print the
username instead.  Is there a way to do this in a template without
having to write supporting code in a scrip?