Reverse bleeding. Can do with a 50cc syringe too...Just in case you or anyone else runs across the utter despair that is bleeding a freshly installed internal slave cylinder in the future:
A few years ago I ran into the same issue after installing a clutch and slave in a mid-90's Saab 9-3. After fighting with it, I came across a procedure on some Saab forum that worked like a treat! It basically goes like this:
Attach a hose from the LF brake bleeder to the slave nipple
Open both bleeders
GENTLY press down on the brake pedal, causing brake fluid to be pushed backwards through the slave (along with any trapped air) out and up to the reservoir.
Close the clutch bleeder, then the caliper bleeder
Pump the clutch 5-10 times SLOWLY
Repeat the above one or two more times
I've used that trick on several clutch jobs since, and while it doesn't always work it has proven to be handy in a pinch.