Ah, I see. So it would have worked the way I said, except when I posted:
function callback_func($key, $value) { return ($value < 2 || $value > 70); }
print_r(array_filter_multi($data, $callback_func, null));
It was actually:
function callback_func($key, $value) { return ($value < 2 || $value > 70); }
print_r(array_filter_multi($data, 'callback_func', null));