This may be a stupid question, but you disconnected it BECAUSE the clutch was stiff?
Only reason I mention is that I made that mistake, once. Pressed the clutch pedal with the slave disconnected, no movement, so pushed harder and broke the master cylinder pushrod.
With the slave disconnected, the "piston" is fully extended, just like if the pedal was fully depressed. If you were to assemble the setup, the piston would be compressed by the clutch fork/pressure plate, and thus would allow pedal movement as the fluid acted on the slave cylinder piston as you pressed the pedal.
