I've been there too man, it sucks. One time, I took the line off of the master and submerged the whole thing in fluid up to the reservoir port. I pumped it many times, ensuring that there was no more air in it. Then I poured fluid into the remote reservoir line and popped it onto the master. I put my finger over the pressure port of the master and screwed the line on. Keeping the reservoir full, I gravity bled the slave, then mighty vac'd the slave, and finally was able to get fluid out of it when I pumped the pedal. A bit of pumping and opening/closing the slave bleeder and it firmed right up.

Rear brakes are even worse... at least there's no prop valve on a clutch line.