I actually have one that I built a few years ago. It was for recording, not a stompbox, but about the same size and shape. I actually don't need it any more....
If you kinda know what your source and load impedances are, you can do it quite readily in a passive deal or a buffered passive deal or some kind of active thing. Look at some electronic crossover schematics -- that's actually what you're building, without the low-pass section.
Here's kind of an obvious but probably very effective one: http://www.eeweb.com/blog/circuit_pr...gh-pass-filter
Heck, you could probably put this in a pedal -- I mean a pedal pedal like a volume pedal body. Just make the capacitors smaller if it doesn't cut high enough. If it wuz me I'd start with capacitors half the size of those in the drawing for a guitar application. You will be tailoring this at the end so make them accessible / changeable.
This is probably a senseless and redundant post but I just woke up.