Is there a way for a single request to be received by all pool members

The HSL method (and sideband method for that matter) would certainly get the AVP message to all of the servers, but that definitely seems like a lot of unnecessary overhead (sending AVP messages to servers that will never see the client traffic). The alternative would probably be some form of persistence. The question then is, what's in the AVP message that could be tied back to the client? Since the GGSN is actually sending the first message and the client is sending the second, is there something in the payload that can be used to correlate the two?