To my knowledge the only way this could be prevented without going to a new build would be to have server-based client-side screenshots
All that needs to be done is when a player joins a server, record the md5 of his mapfile, if anytime during the map the md5 changes, he's cheating and notifies the GBL. Such a change would be very very minimal and would not need a new build.
It would take an hour, maybe two, to add this to the cheat detection. It is still possible to use this cheat, however Jitspoe has known about it for almost a week and a half. Which means that anyone that's used it in that time period has probably already been detected, and anyone who uses it from now on will definitely be detected.
In the very near future there will probably be a mass-ban for anyone who has been using this hack.