Just another idea on the route to contruction, I built my own for my cab about 3 months ago, a real nice addition.
Instead of going with the pvc pipe thing though, I stopped off at a local bike shop and picked up 4 motorcycle press on handlegrips.
That, and 4 standard arcade PB's, (the ones where the cherry switch sits vertically though) and a little whittling, and I've got some fairly comfortable buzzers.
I've got to get to updating my cab page one of these days, I've documented the whole shebang, but haven't had a chance to WebAtize it.
SD