It doesn't seem to be an upload rule that you can't upload upscales right now, so the first order of business seems to be that the rules should be changed to allow downscales for people who don't wanna spend the bandwidth, but it should be against the rules to upscale.
Then you still can't detect em all, but it is fair to warn users not to post upscales.
Another thing you can do is make people declare whether the torrent post is a rip at the original resolution, downscale or upscale, and if they submit with upscale selected you just eat their submission and time them out. ( you don't just want them to go back and lie, so giving them a 3 week freeze on download and upload will probably make the point)