Most of the options you have been given require grip strength.
Never put a cue in a vise, unless you're willing to destroy your cue. I can't remember, off the top of my head, if Mezz uses a weight bolt with a shoulder on it (can you see the weight bolt?), or if they use a set screw type. I remember them has having a threaded bumper, with a set screw.
You need leverage to break the seal. I have seen gasket sealer on some weight bolts. Having something rubber, like those round discs they sell for opening jar lids is a lifesaver for this. A T handle hex wrench helps, too. Standard hex keys are too short, and you can't apply much torque.
I've removed weight bolts from every Mezz I've owned, and I don't remember it being too much of a chore. Let us know how you make out.
