
I think the auto down switch is a 3 way potentiometer type thing which means you can't modify it to do an auto up as well. Even if you could, you'd have a fair bit of effort needed to pull the plastic bit apart to get to the plastic switch and make that a four point switch rather than a 3 point.
Although it's possible, it requires a fair bit of reverse engineering, and even then you'd need a custom PCB to accomodate both sides having the proper potentiometer type thing.
It can be done, but will require a fair bit of effort. It'd probably be easier to build one from scratch rather than try and reuse their parts...