Here's an idea: The joystick up/down outputs are summed together to create the vertical axis output value. We split the axis into two directions and then sum them up like this:
vertical axis = right_joystick_down - right_joystick_up. When the joystick is up, the output is -100%. When the joystick is down, the output is +100%.
The rows are summed together.
You can use sensors other than the joystick for the axis, like the sip/puff inputs or the lip button.
You can repeat the rows to add more to the direction you want to make more sensitive.
right_joystick_down, normal, down
right_joystick_up, normal, mp_center_puff
right_joystick_up, normal, mp_center_puff
right_joystick_up, normal, mp_center_puff
...
repeat as necessary to make the up movement "snap" when you puff.
Play with the sip/puff max setting too. The lower the max pressure, the faster it will reach 100%