I'm not making you do anything just giving you suggestions.
The need for this disclaimer is probably the first sign that it's bad advice.
Anyway, I'm sure this isn't the answer you want to hear, but have you tried loud, aggressive behavior? Animals (including people) tend to assume other animals (also including people) will act according to the situation, which means if you act like you're weak and/or prey, they'll assume you are, in fact, weak and/or prey. If you act like you're strong, they'll assume likewise. This is why the advice for dealing with dangerous wildlife is never just "run away as fast as you can"- it's not just that they're faster than you, it's that running clues them into the fact that they've got you and should give chase.
So on that note, simply puffing yourself out a bit and shouting at them if they get too close (or don't move out of your way) might help more than you think. Eye contact is also challenging, so look them right in the eyes if they seem like they're buying it. Basically, imagine you're a bigger dog, and bark accordingly.
And yes, I realize this advice sounds rather silly, but consider what happens when a human marches straight into a room and starts authoritatively passing out orders- generally speaking, everyone assumes he knows what he's doing or else he'd shut up. Conversely, if someone's confronted and he panics or looks nervous, people tend to assume he's been caught at something. If you assume people are at least as smart and socially savvy as dogs, it would seem to follow that this should work at least a little.