Vacation flag/automatic "forwarding" of tickets


I’ve setup RT3 for evaluation, and I’m looking for a way to
automatically forward tickets.

Imagine, Customer Care Agent Joe is on vacation, and by accident,
someone assigns a ticket to him for further processing.

What’s the most straightforward way to implement a vacation system? Add
a Custom Field to the User (e.g. substitute) and a Scrip that will
change the owner to the substitute if someone assigns a ticket to Joe?

Thanks for any hints