How to assign an extension to always use a specific trunk

I remember seeing this a few days ago. Someone has posted the same questions, but I can not find the thread.

I am looking to set one of the extensions to use a specific trunk for all outbound calls by default. I know, I can do this with dilaplan/prefix as I have done that before, but if I remember correctly the above mentioned thread shows an easier way of setting this up. Please point me in the right direction here. Thanks,