A "fun" workaround would be to print a very high resolution black-and-white checkerboard. Printers generally have plenty of resolution to make that appear as gray even to the naked eye. Of course managing to print something like that without something in the pipeline trying to anti-alias stuff and introduce gray back is left as an exercise to the reader.
- there is no such thing as perfectly black ink
- color printers will mix color ink into greyscale printouts