The 515 is a mechanical brake, last I knew. I'll assume you do have a hydraulic brake of some sort... you don't need to have the original bleed block to bleed the brake.
1. reset the pistons. Clean up a blade screwdriver with alcohol, slip it between the brake pads, and gently force the pistons all the way apart.
2. remove the brake pads and put them somewhere they won't get contaminated.
3. take a wooden wedge shim, the kind you use to level furniture on uneven floors and stuff, and saw off a couple pieces that are small enough to pass completely through the brake caliper. Use them in opposition, to wedge the pistons apart.
4. bleed brake
5. remove wooden shim things, clean up the brake thoroughly with rubbing alchohol, and install the brake pads.
6. install the wheel and brake rotor and squeeze the brake lever repeatedly so the master cylinder can bring the pads in.