Use an existing users mailbox for Bookings/URL

It doesn't look like this is possible, but it would be great to allow Bookings site\mailbox creation for an EXISTING user.  As I understand the process now, if you have an existing user (say, UserOne@) and they need to provide a personalized booking page to a client, we would need to create an entirely new Booking site for that user.  We will call that Bookings site "useronebooking@".  The problem here is the solution creates a brand new user account in O365.  If we wanted to approach this from the perspective, each and every new sales person would consume two O365 accounts; one which is actually licensed (userone@) and the other that is for Bookings (useronebooking@).  I suppose it isn't the end of the world but certainly creates some clutter when thinking about management.  Or, maybe there is a way around this and we can leverage an existing account for Bookings.  Anyone have the same issue, found another way, or agree on my thought process?