Persistence based on a server id url param

I've got haproxy set up (with 2 frontends) to load balance a php app which works great. However, we're using a java uploader applet that doesn't appear to handle cookies. It would be simple for me to have the uploader use a URL with the server id in it (just like we're already doing with the session id) but I don't see any way to get haproxy to treat that parameter as the actual server id. Using hashing is not an option as changing the number of running application servers is a normal occurrence for us. I also can't use the appsession directive as the haproxy session id cache isn't shared between the two frontends (both running an instance of haproxy). Can this be done with ACLs and I'm missing it?

Thanks,
Ryan

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Ryan Schlesinger
President
Instance Consulting Inc
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