Buy CPUs from two (or n) different vendors and run a user space lockstep execution virtual machine between them. Unless all vendors are compromised in exactly the same way, the output will fail to verify.
Of course, this would prevent you from using RdRand as your VM implementation will only be able to call on deterministic instructions...
Of course, this would prevent you from using RdRand as your VM implementation will only be able to call on deterministic instructions...