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.