Just an idea from DOTA. You can buy 'phase boots' and activating them grants a few seconds of no collision.
It would be neat if the ACU had a phase shift (no collision) button for when it gets trapped between engies. Just a few seconds so it can escape. I don't think it would introduce any balance issues.
Whether this would cost anything (small energy cost perhaps) or would work for other units like SACU is another question we can discuss.