I went down the rabbit hole on historical instruments, something that I haven't paid too much attention to, and found out about the violone and lutes, especially how the frets on these instruments are basically just gut string that is tied around the neck. Long story short, I got some 0.7mm nylon string and it works perfectly fine without any modifications to my bass. I'm not suggesting that this is a serious endeavor but it's really fun to play your upright as if it was a fretted bass guitar and at 3 bucks and half an hour of fiddling around with some string it's just plain fun without any real investment. Maybe this is old news but I just found out about it and I think it's really neat.