Just bringing this back up because I can confirm this works for Sucuri. I recently switched one of my old vB forums to XF. I have Suruci on that site and all my visitor IP's were showing Sucuri IP's instead of the true visitor IP.
Following step 7 in Brogan's link above and editing the config.php file did the trick.
Just one small correction on that FAQ page. It says the file location is library/config.php which is incorrect. Correct location is src/config.php