This little gadget from DW allows you to mount a hi-hat or other stack to your bass drum. It comes with a clamp that attaches securely to both sides of a bass drum counterhoop (designed for 18"-24" diameter drums).
There is a height-adjustable arm with a variable tension hi-hat clutch, so that you can quickly affect the tension on your stacked setup. Use this to expand your setup without taking any extra floor space, and add some flair to your sound pallet!