You can't reliably circumvent them unless you manage to at least obtain the source code for all of Windows and recompile it. (And even then I have some doubts.)
If a program requires SSE2 or something like that, it is generally because it was compiled to use SSE2 instructions – in which case bypassing the requirement checks would mean the program would crash as soon as it reached a place where those instructions were used, because your CPU didn't recognize them. (Having that happen for the OS itself wouldn't be nice, would it?).
Sometimes Windows has code for CPUs both with some feature and without, and detects the supported features at boot time – but I doubt it would bother doing that for something that was listed as required in the first place.