I have, in the past, been forced to type an Xmodem transfer program into debug.com's hex mode, to get to the point where I can transfer files over a null-modem connection from another box. I can dig up the file in question, if that'd help you out at all.

I ended up typing it in 1k at a time, and independently typing in a CRC32 utility to check that I'd done it properly.

(That was to install Windows 98 on a computer with no drives, if I recall. So, not so very long ago.)