I don't have my Bandit handy- what does the knob attach to? If it's a threaded rod sticking out, it couldn't be easier to fix. I just made a replacement knob for the tripmeter on my son's EX500. I found a metric tap that was the same thread, drilled and tapped a small round metal disk of an appropriate size, and glued (with JB Weld, naturally) a Schrader valve dust cap over it, job done.
If you're less concerned about keeping things stock you can skip the drilling and tapping and just JB Weld something onto the stub shaft.