Abs Noobie Adding a customer account to an existing domain Pl'sk 12

[MSSB_Consulting]

I need to allow full administrative access to a developer to one of my domains in Plesk 12. I've tried adding a new administrator but this is a global privilege, I've tried adding a customer but I cannot do this against an existing domain. In previous Plesk versions I seem to recall you could simply add a user under the domain.