Got a reply from a very helpful chap within the company:
Sorry but this is working as designed...
BlackBerry ID is designed as a one person to few devices facility (ie BlackBerry and PlayBook).
We in Enterprise have explained the difficulties some Enterprises have in trying to set-up multiple devices on behalf of the users but been informed BB ID is an integral part of BlackBerry Balance, PlayBook, etc and it is important moving forward so no work round.