I've heard that two different Torx bits fit the pivot screw, T30 and T25. I have several Kizers with the proprietary pivot hardware, but my biggest Torx is a T20. I've meant to pick up some bits between 20 and 30 to test this out, but keep forgetting. Anyway, you might try that route. If your pivot is on one of the older 4 or 5 series knives I think it might be a T30. The older 3 series knives supposedly use a T25...
But again, that's all based on intertube rumors...and we all know the internets are the truths!
I'll see if I can find some big Torx bits to confirm this rumor...