I bought a 20-pin dual-USB 3.0 adapter from eBay, and the jacks interfered with my DIMMs. The solution: bend the female header over (see photo). It's still untested, but it probably fits… UPDATE: It's plugged in, and my computer booted fine. Still haven't plugged a device into it, though.
At the request of a friend (who also funded the endeavor), I designed and built three cables which allow one to plug an SNES pad into the Virtual Boy. The two controllers are basically the same, electrically, so the adapter is entirely passive.