Simon,
Assuming everything is ok with the clutch - it's not execessively worn, right springs, right pressure plate and cover, proper linkage arm lenghts - you might try a smaller diameter master cylinder. Less fluid moved per measure of pedal travel should put the engage/disengage point further down in the pedal travel. The side effect will be lighter pedal forces. Just make sure that you do get disengagement. Going too small could prevent this.
Changing the master cylinder sizes is analagous to changing gears: holding the slave constant, the smaller you go (lower gear), the more pressure you can apply, but you'll have less travel at the slave. The larger you go (higher gear), you'll have less pressure but more travel. (This is true for hydraulic brakes as well and a good thing to remember.)
Regards,
Lynn