This is just stupid. I already dislike software with locked features that can be enabled by paying extra, but at least you can argue that 99% of the price of the software is in development, and distributing different versions would actually increase the price. I can't imagine developing the extra cache costs more than the die area, and it's not an issue of yield either (they are already certified to be stable with the extra cache/hyperthreading, since they don't any testing before activating it). You're just paying for market differentiation. At least for the Rigol scope, they may have more stringent specs and do calibration all the way to 100MHz.
I wonder where they store that information. As far as I know, CPU's don't have any persistent storage (unless they included some EEPROM for the first time). Modifications like this are usually done by physically cutting traces on the die before packaging. Patching the BIOS would work until the processor gets separated from the motherboard (probably not that likely given the market for low-end CPUs), assuming the BIOS updater understands to leave this area alone (like it does for SLIC certificates). Patching CMOS memory would be destroyed when it's reset or the battery runs down. Installing a service that's run at startup would preclude it from working with any other OS and require reinstallation after reloading Windows (or replacing a hard drive).
I'm not sure how much interest there will be in hacking this, since the overclocking community typically isn't that interested in low-end CPUs. It's probably not too hard if you analyze what the upgrade application does for someone with time and skill.