Berkley,
There is a way to do it with a Phone Manager client, but not a simple way to do it otherwise. I assume they would want all extensions with that capability. This assumes they have trunking that allows for CPN substitution.
***Extra***
What I have done in the past is created multiple CO Trunk Groups and split their lines up evenly between them or they had multiple PRIs and set the CPN to force a particular number and then gave each phone a CO Trunk Group button that lets them grab a channel and call out.
Thanks,
TE