Have you tried to bleed the clutch by pushing fluid through the slave first. Basically backwards through the system?

If you can hook up to the bleeder on the slave cylinder, you may can push the fluid back towards the master cylinder. I have very good results with that when hydraulic clutch would not bleed.

Another thing that has worked is setting a pan under the bleeder and just opening it letting the fluid flow through the system by gravity. Have someone watch the fluid level as it drains and keep it full till there are no bubbles.