Force IIS IP Filtering to read an alternative value for incoming traffic ip

Is it possible on IIS6 to force the IP Filtering module built into IIS read a client ip field inserted into the header by an isapi filter and use THAT for the filtering basis? I'm thinking no..

Situation: proxy server in front of webserver is causing IIS to read the proxy server's ip for filtering purposes. Easy enough to write or use an existing ISAPI filter on the market that will pull the real ip address from the x-forwarded header and use that to write to the logs, or similar action. But can i do something in my ISAPI filter that will FORCE IIS IP filtering module to see a value i want it to see instead of the real incoming ip of the proxy server?