the best way is to backfill them with some tubing and a syringe. If you cant find a syringe, take two pieces of tubing and put them in jars or something with brake fluid in them. Elevate them above the bleed valves. then bleed them as usual. Meaning, open the bleed valves, then slowly press and release the brack valves until there are no air bubbles anywhere in the line. You will know you did it right if you have brakes as soon as you close the valves.
or what you can also do is to take the calipers off their mounting bracket and push the lever a little to make the brakes go in, let dit for ten seconds or so then squeeze the pucs back in and force the fluid back up to the master, do that repeatedly until no more air comes out. one side at a time
Just went through the same problem myself putting on my stainless lines and YFZ calipers. The biggest pain was getting all the air out of the master cylinder. It may just be my setup, but if I turn the handlebars to the left, that puts the master cylinder at its highest point, then using very small movements of the brake lever (only moving the end of the lever half an inch maybe), I slowly worked the air out of the master cylinder. After that, it was simple to bleed the rest of the system in the usual fashion.
there a bitch to get all the air out if u don't u can spend useless time on it doing so.
put your finger over the hole on the master cylinder and start pimping till the brake lever
gets stiff. that's one way or like said befor get the master cylinder to
highest point to get the air bubble's out.