The way I see it: It's effectively illegal to prove the machines are fraudulent as they are proprietary machines and are closed source. So, given that they are run by partisan companies and we have absolutely no method of verifying their inner workings:
Don't we have to assume that the machines can't be trusted?
Analogy time. If one left a partisan alone with unsealed boxes of ballots, I would think they would be considered spoiled (correct me if I'm wrong). I agree with you that leaving the electronic ballots in a partisan's computer with no mechanisms to detect tampering should similarly be considered spoiled.
A strong paper trail seems to be the answer. It doesn't matter what the hardware and software tries to do if the machine has to produce a paper record (checked and approved by each voter) that is spooled for later checking against the electronic total.
I mean, if this were true Romney would win. What's the point of rigging machines if you can't swing the swing states in your favor?