I believe the B&H mousetrap was more to increase the travel of the clutch release arm so the clutch would break Free. A hand lever alone barely makes it.
there's a thread about this somewhere. The auxiliary clutch kit supplied on WLAs in the UK is pretty poor. The geometry of the lever and actuating arm doesn't provide sufficient lift, but this can be improved by redrilling the arm to provide more travel - the cable hole needs moving closer to the pivot so that the same cable travel provides more angular movenet at the arm and hence, more lift on the release pushrod.
Shoot, a man could have a good weekend in Dallas with all that stuff...