I had the same trouble when I did the slave cylinder on my other GU so this is how I got around it.
I fitted a plastic hose to the bleed nipple on the slave cylinder and ran it to a jar with a bit of brake fluid in it so it covered the end of the hose.
I opened the bleed valve then placed my mouth over the fluid reservoir and blew into it as hard as I could for several seconds.
I could see the level dropping as it started to siphon through so when I saw the level get near the bottom it topped it up and then closed of the bleed valve and topped it up again.
Don't touch the clutch pedal until after you've bled it and tightened everything up again as that stuffs things up and you have to start again.
It worked perfect after that .
