If you're working with a template (for joystick or trackball mounting), you can use the same flush trim pattern bit. If it's a bit with the bearing on the bottom, you can drill a hole to start routing.
And if you buy a bit with the bearing mounted on the top, you can even use it for through holes like a speaker hole, assuming the cutting length is deeper than your material, of course.
Or, you can buy a straight bit, which essentially looks like the pattern bit sans bearing, *or* a spiral cutting bit.