I see that everyone wants to bleed the brakes using the most time consuming and difficult methods.
1. Leave everything mounted as it should be.
2. Go to local pharmacy / drug store and purchase 2 large syringes that hold at least 30cc of fluid. and purchase some clear surgical tubing from them as well, about 2 feet is more than enough.
3. Use 1 syringe to suck all the fluid out of the master cylinder and dispose of it in a disposable container.
4. Using the 2nd syringe attach about 12 inches of tubing and suck up some new brake fluid.
5. Attach the tubing and the 2nd syringe to the bleeder on the caliper, and crack the bleeder.
6. Slowly inject the fluid in thru the bleeder while having someone hold the brake pedal slightly depressed. I just put a 1 quart paint can on it.
7. Close the bleeder and refill the syringe.
8. Repeat steps 5 and 6, watching the master cylinder for bubbles and remove excess fluid as required.
I have done the above procedure on a lot of friends bikes with "useless non working rear disk brakes" and every one of them has ended up with an excellent rear brake. This procedure is simple and once you do it, you will be very surprised how easy it is to get a good solid pedal, and a brake that will actually stop the bike.
I also use this same procedure on front brakes if I have had to remove any lines, or I just can't get the spongy feeling out of them using the normal methods.