UBB.threads PHP Forum Software Community Forums Resources and Customizing How Do I? Logging users by the X-Forwarded-For IP instead of our proxy IP

We just moved out forum box behind an F5 loadbal/proxy, as part of getting all our machines behind it, even if they aren't load balanced. However, now, all members are logged by the IP of the F5 rather than their origin IP. The F5 is sending the X-Forwarded-For header correctly, but ubb doesn't seem to use this.

How can I config ubb to log members based on the X-Forwarded-For header rather than our proxy address?