It's a slight exaggeration how frequent parens are used in Lisp. The keys tab, space, shift, backspace, hyphen enter are probably used more often, and many alphanumeric keys.
Perhaps you could have the whole keyboard floating on a pivot like a see-saw, with one of these switches beneath it at the right and left side of the pivot (say beneath s and ; keys). That way any key press off-center would have a chance of activating one of the two switches, and keys closest to the far left and right would have a greater probability of activating them. The keyboard would have a slight wobble.
Perhaps you could have the whole keyboard floating on a pivot like a see-saw, with one of these switches beneath it at the right and left side of the pivot (say beneath s and ; keys). That way any key press off-center would have a chance of activating one of the two switches, and keys closest to the far left and right would have a greater probability of activating them. The keyboard would have a slight wobble.