This actually ended up saving my Domino. Due to excessive strain I ended up breaking off the micro-usb connector. At first I resoldered the pads, but they didn’t hold. Then I thought “the board runs at 3.3v, and is fed 5V from the host. I wonder if the slave USB is just directly connected.” So, I made up a pin header to USB adapter, and lo and behold, it works.
This might be useful for people looking to build a headers-only hookup for their Domino Pi to attach to another board. No need for an extra micro-usb cable sticking out, although I don’t think the USB-serial adapter is broken out anywhere else. So, if you need to use the jtag rescue or want USB-Serial you’ll still need the micro-usb hookup. (Unless it’s a single OTG port, but I don’t think it is)