DISCLAIMER:
Will not fit all 400 pin breadboards! There is no underlying standard for them all. This is designed around the 400 pin breadboard supplied by Adafruit, with 1.5mm clearance.

This has enough overhead space to fit a very tightly bundled set of wires, while they are the type that stand right out of the breadboard as pins.

To mount to anything, drill holes in the bottom and screw it in, or use double sided tape, glow in the dark gluestick, glitter glue or whatever.