not sure about the GS, but owners of early R1250RS with the colour LCD had the sports screen added free as part of a routine firmware update, usually when they had a service
What's it look like? Seen some other screens on Facebook on GSs where folks have said they have programmed them to do it, but no explanation as to how.
I also enquired and they sent me some more screen shots, so it looks like you get another option in the bikes menu, and you can select the type of screen you want displayed, see attached: