Here's a thought, a thought from way back before these computer tools we have made things easier.
The time before fax machines, the time when photo repro blue, frisket, amberlith,cutting films all were status quo. They were getting one's chops the hard way. This was the time that there was much more craft in graphic design than there is now..What if I refined my sketches to the point that they were ready to go, but needing to be finally inked. And, as you know, taking them into illustrator freezes the spirit in them. So, what if I were to scan this illustration and change the coloration to photo blue (non-repro blue), blow the image up to 300% of final and output on the epson on enhanced matte paper. If this wouldn't do, we could try one of the watercolor papers primed for this. Then, to do the final, to work up all the line work and outline on the output ..keeping the big fields of black for the second scan (back into the computer) to add black for fill? Reduce it down and away you go. Keep it really high res for future use as one can always subtract pixels and make something smaller. It doesn't work the other way around.
This makes sense to me. I should give it a try.