Basically , VAC is using ReadProcessMemory right to scan the game process, well how about hooking that function with detours and changing the process handle to scan for another MW3 copy thats clean and updated, i am not sure if you can run 2 MW3 at the same time?, if not run a copy from another computer and make a basic TCP client/server that sends the clean MW3 handle to the hooked RPM function then it will be scanning the clean game right.