Defaulting purchasing group from drop-down

SRM 5; 46C R/3; Classic Scenario

Hi experts,

Is there a way for me to control for each user - the default purchasing group? For example the user has 3 purchasing groups to choose from. It always defaults to a specific purchasing group. Is there configuration setting somewhere that this can be changed to another purchasing group as default value? User Profile in org structure?

Any help would be awesome.

Points will be rewarded!

-Felix