I couldn't find any other topics showing this mod done, and although it is not a particularly hard mod to do I wanted to share my results of adding a Famicom 15 pin connector to a toaster NES:
It was fairly simple to do, the main thing to figure out was the wiring, since the bottom of the EXP port is under the toaster's cart slot. I took an old IDE ribbon cable and stripped off 15 wires from it, and pulled back individual strands on both ends, the middle was able to lay flat beneath the cartridge bay without issue. Enough length was left so the board can be lifted again later if needed, and the other end soldered to a standard DA-15 connector mounted in the front next to the controller ports.
My Bandai Hypershot, and Tap Tap Mat accessories worked fine with the connector. Although it isnt as deep as the DA15s on Famicoms and Neo Geos, the connectors fit snugly and don't move at all. I plan to get a set of Famicom 3D glasses next to try out with it.
Has anyone else tried this mod? If so, share your results!