In that situation, it's worth trying to find another way. Changing the slave is a lot of work.
Vacuum fill might work if you can figure out a way to actually do it. You can't pull a vacuum on the resevoir line because it is just going to collapse. It's also on the wrong side of the master cylinder. You really only need to bleed the slave this way, but the issue is how to connect to it. Most likely, you would need to add a tee with a valve in the middle of the line from the master to the slave. You could hook up a vacuum pump at that point and pull the line down (which hopefully can hold the negative pressure). A couple valves would let you seal off the vacuum and connect a fluid supply to refill the system. You would really have to watch out for air pockets in the plumbing since there isn't much volume in all the lines. But if it works, it might be a good way to get the air out of the master lines too.
If you get something that works, post some pictures for us. I expect you will soon be changing the slave though.