Default Org Key based on Position?

My company would like to default org key based on the position. In feature VDSK1, I would not be able to choose position (nor would I want to list all of them anyway....). Originally I was hoping to create a custom relationship in PP01 that would link Org key to position, but since org key does not have an object number associated with it (it's simply text), I am not sure how I can set this up.

Any suggestions? Thank you!!