I got fed up of my clutch pedal being unpredictable like this, so I totally flushed out the old, dirty fluid with new stuff - it took ages (at least an hour) and I flushed about 2 jam jars fo fluid. I used the "new" method I found on youtube and the clutch is much better now.
heres my post - Having problems with my clutch - bled the slave, but the problem was soon back, then found this
This guy seems to know what hes talking about - and from memory of the system on the z i think it may work