Been there, done that.
What finally worked for me was the syringe trick, but from the reservoir, not the slave.
I was lucky to find that the top of the break fluid bottle ALSO FIT THE RESERVOIR!
I drilled a hole in the top, large enough for the syringe to fit in, and injected fluid, under pressure, though the line with the bleeder open.
There may be other ways, but that worked for me after many previous attempts and verbal assaults on common decency.
Good luck!
On their death bed, nobody ever said, "Gee I wish I'd spent more time at work!"
'68 Sprite 1275
'76 Midget 1500