To challenge the ban on public transit carry we need a plaintiff that for some reason can't drive, but is otherwise OK to pack. Please God NOT because of DUI convictions! Lemme think...epileptic? (scratches head)...amputee of some sort? Or some other wheelchair-bound individual?

The other answer is to prove that blacks take the bus in higher numbers by proportion, that this was well understood and that there's a deliberate racial bias in the rule. Call it the "Hunter v. Underwood" attack:

http://en.wikipedia.org/wiki/Hunter_v._Underwood
It'd be hard to prove that was the intent though. Pretty damn obvious what the barsterds were doing but...the courts would want proof.

The final option is an equal protection "scrutiny test". Get it bumped to strict scrutiny and it's a win as many other states allow packing on public transit with no problems. Intermediate...hmmm...might still win. Rational basis we'd get reamed.