Filling the brakes with hydraulic fluid was a job I often thought of. Having done this never before, some consideration was made how to perform it. In the end it was an very easy job. Take a simple oil can with a small tube, connect it to the bleeding inlet at the bottom and insert the fluid from the bottom. I used simple automatic transmission fluid from the automotive store.
The left brake was quickly filled with fluid. The right one was not so easy, I could not get the fluid in. In the end it turned out that the cylinder at the brake was so far in that the bleeding inlet was blocked. Thus I filled the tubes just after the caliper, then connected the tube and did a single braking. The cylinder at the wheel popped out and then I could easily bleed it from the inlet.