Wow, you have a "real world" stumper there, considering the temporary nature of the hookup. I think you are on track about finding a way to ground things out, but the problem seems to be that you can't rely on some cold water pipe and its bond to the panel for a ground...unless you have traced it all out and you definitely can see that such bonding is complete and things are connected tightly (though it wouldn't be code to be doing this, in your world, it seems to be the practical choice to make). As far as the outlet being ungrounded, except through a neutral, that scenario only held for residential work, not commercial, so there should be a separate equipment ground at that 220 outlet. My guess is that the outlets were an add on outlet, and probably wasn't inspected, so who knows how it might be miswired?
What's a "distro"? Just a box for multiple 120V plug-ins?