Just wondered if you had succeeded yet?
I've the same prob (YZF750 too), tried pulling lever half way, tried with brakes off the bike on a bench, calliper sideways, calliper bleed valve upwards, tapping them, pistons pushed and held in with packing, lever tied up for days, new master cylinder seal, just about everything I can think of that's worked on other problem bikes.
Have braided hoses so not sure if I can clamp.
Any other advice please?