You can unscrew a brake hard/soft line junction and add a plug/block that will hold brake pressure and be less likely to get knocked loose than the vice grips.
I've successfully used a nail that was inserted into a brake fitting to fully stop leaking and hold full brake pressure in an emergency / make it home situation.
How to with a nail: Find the easiest fitting to take apart on the line/circuit that is leaking, unscrew the brake fitting/junction and then if you have a nail that's the right size you put it into one side of the fitting and then screw the fitting back together. The shaft of the nail keeps the head in place/centered and then the clamping force of the fitting seals things closed. A thinner head nail that is the width of the mating surface inside is ideal. Don't over tighten the fitting as it could damage them. I'd loosely assemble then bleed the air out of that line before snugging it down just tightly enough to stop leaks.
Short of a nail you could use a similar technique with other materials. Cutting a disk out of a rigid/durable plastic sheet of some sort could work well and be less damaging to the mating surfaces on the end of the hard line. It's more likely that you have a suitable material to make a plug out of than an appropriate nail. Follow the same procedure where you leave the fitting (with plug) loose until you've bled the air back out of that line and then snug until it stops leaking.
Good luck!
