It might be OK if you could get it to the right length and not have it slip.
3-speed hubs are extremely sensitive to cable adjustment. The hubs are bulletproof but cable slipping or stretch is a big deal -even a little bit will throw off the shifting. You don't want to find neutral by accident. I hate it when that happens.
I've heard of people who have claimed to have tied a knot in them successfully. I've never tried it. I say it's not a big deal to experiment but be careful about how you use the bike until you are sure that the cable isn't going to move and you can be certain that you won't find neutral and end up hurting yourself or biting your handlebar stem as you slip off the pedal unexpectedly. Cosmetic dentists are expensive
