Hi Martin,
I don't have that function available in my system (EHP6 SP7) in the customer version of transaction BOB. I've looked up for a way in transaction /BOBF/CONF_UI that is intended for internal use by SAP and there's a workaround to activate this function. Nice to hear, that it will work in customer environment and I assume that creating alternativ keys is also a requirement for your development.
This leads me again to the question why it is not intended to be used in customer environment.
Regards,
Kai