Scott,
Priority groups is probably what you are looking for. In a nutshell, you can put all of your servers in the same pool and assign a different priority group to them. All traffic will route to the highest-numbered priority group until the number of enabled servers in that priority group is less than the value you specify for Priority Group Activation. For example, if your pool consists of two pool members, serverA with priority group 2 and serverB with priority group 1, you will want to set your Priority Group Activation to 1. All traffic will go to priority group 2 (serverA) until it becomes disabled, then all traffic will go to priority group 1 (serverB).
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Kris