How about a hat with one of the band logos duplicate stitched onto it??? I've only delved into the scarf and hat world myself, but I learned how to do duplicate stitch and it is sooooo easy!!! :-D Here is the article I used: http://www.purlbee.com/duplicate-stitch/
The best part of it is, if you do a hat (as opposed to a scarf) no one will be able to see the reverse side! Of course, I would probably pick the logo that was the easiest to recreate on a knitted object. Or if none of the bands have a logo, maybe stitch the name of one of them? Or maybe a simplified picture of the instrument he plays (or a mic if he sings)?
Good luck with whatever you decide to do!