http inserts while using SNAT

I use a basic irule to insert the originating clients remote ip address in to the header (irule below). This works great for proxies and servers directly behind my F5 that I am NOT using SNAT with. On VIPS that I do use SNAT how can I get this working? I need to pass the originating clients remote ip address to the backend server that exist on another network while using SNATs. Any Help?

when HTTP_REQUEST {

HTTP::header insert_modssl_fields addr addr addr

}