Jeremy,
It is possible to dynamically build that list based on, say, a data-dip. I did a webinar on how to do it a while back for Beyond - if you have a subscription, you should be able to go back and watch it. The example I used was where customers had a primary contact and a secondary contact within a team. The call would go to primary, if possible, then to secondary, then to Team and finally to anyone.
I'm a little confused by your comment concerning 1500 agents. What is it you are trying to do? Preferred Agent is essentially dynamic bullseye routing, so there are a limited number of "Rings". Are you wanting to statically assign preferences to all Agents? If so, then you would probably be better off just using Bullseye.
HTH
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Paul Simpson
Views expressed are my own and do not necessarily reflect those of my employer.
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