The only thing I could come up with is pushing it’s eyes in - I know that sounds grim and cruel - but if it’s an XL Bully then it’s quite literally life or death and in that moment I’d do whatever I felt necessary.
Probably won't even make them flinch if their aggression has been triggered. It sounds bizarre, but think of them a bit akin to zombies in that state. Only death or incapacitation will make them stop. The kind of pain that may make a regular dog give up and let go will not work. These things take multiple gun shot wounds before dying.
How good is your aim? Because you will probably have to push something like a screw driver in far enough to skewer it's brain.
People around here have started carrying objects they are 'meaning to give to their mum' or 'forgot to take out of the bag when they were doing some DIY'.
Though honestly I think you still stand very little chance unless you are used to using weapons, at least 6 foot and built like a shithouse, AND very very quick.
It's just something people who (rightfully) feel helpless to protect themselves do to feel a little better when out and about. You also have its fierce intelligence to contend with, make no mistake, it may be on your arm, but it's eyeing up your throat and looking for a split second chance.