Have you tried this? I've posted this before so this time I'll just copy it here.

BLEEDING BRAKES.

I've been working on bikes since before they had disc brakes. I usually drain & refill mine at least once a year so I've had lots of practice.

I get a length of 3/16" clear tubing long enough to reach from the bleeder screw to the master cylinder. I fill the m/c, put the hose on the bleeder screw & open it about 1/2 turn & hold the free end of the tubing in the fluid in the m/c reservoir. Keeping the free end down in the fluid, I slowly pump the brake lever until I have a solid stream of fluid in the hose. I then close the bleeder screw & remove the hose from the bleeder. If you clamp the hose just above the bleeder before you take it off, you won't even make a mess. This has always worked for me & gives the firmest lever of all the methods I've used for years. It works because when you release the lever, it will draw fluid into the hose & not air, & when you squeeze the lever the air will bubble out. Just keep the free end IN THE FLUID so you don't draw air in.

Between my 2 bikes & my friends, I do this several times a year. It even works for rear disc brakes too, as I found out when I did my V-Star 950 the first time.

I first came up with this idea in 1980 when I put a disc brake front end from a '72 Norton Commando on my '70. After spendng a frustrating day going through the m/c & caliper, cleaning & rebuilding both, I still couldn't get it to work. I tried this & was done in 15 minutes. You don't forget what works when you've been as frustrated as I was that day.

Its hard to get the fluid to go into the pump part of the mastercylinder on a completely drained one, do as the last guy said or put some vacuum on that tube & pull the fluid into the guts of the MC,
I had to slightll pressurize the MC reservoir to get minbe to go, Ill never drain one completely again,

most auto parts stores as well as harbor freight and such have one man vacuum brake bleeders that you can buy.

I expect a big syringe would be enough to get it started,,I hate to see anyone spend $$$ on a tool they rarely use..
Engines running create vacuum,

If you have a vacuum source you can poke 2 holes in a mason jar lid & solder 2 pieces of tubing in. One goes to hose from caliper, other to vac source. Keeps you from sucking fluid into the vac source. & lets you see. A piece of clear tubing hanging off the brass tube coming into the jar lets you see bubbles in the fluid.

A compressor from an old refrigerator/ window unit,,can be used to pull an AC system down. Theyll sure pull fluid thru a master cylinder.

A small compressor can sometimes be plumbed out to pull a vacuum.
I cant say if thats bad for them over time, but I doubt it would hurt anything in the 10 minutes youd need it.

With about 4' of clear hose, you could just suck on the end until you can tell from a drop in the fluid level it has started taking fluid. I've never had to, but it would probably work. Over the years i've had several vacuum pumps with the accessories to bleed brakes, but they never worked well. I had much better luck with pressure bleeders, but you have to have the correct adapter for each m/c to use them.

If you now see fluid movement just use the hose like I outlined & pump the lever. You will be able to see the bubbles leave the line until it's solid fluid.

Is this just so simple nobody wants to believe it?