Since I don't have your particular UCS section, I am somewhat reluctant to suggest this. But in the absence of any further advice, consider the following.
Part of the problem is there are apparently different versions of the UCS. I think the term "UCS" is used generically and hence might refer to a variety of products from Lionel and even other track manufacturers.
BUT, suppose you have the style on top of the above diagram.
Apparently you have no use for the "COIL" or uncoupling function. As I understand it, most UCS tracks have the interesting feature of activating BOTH the uncoupling coil AND the unloading control rails together. So if you don't need/want this feature, I believe you can use a simple 2-terminal on-off switch (pushbutton or momentary toggle).
While you wait to see if someone more knowledgeable responds, you might try this simple 5-minute experiment. This assumes you have the style of UCS in the top of the earlier diagram.
Step 1. Connect the "orange' wire as shown.
Step 2. Place an unloading operating car (coal car, etc.) on the UCS and momentary touch the blue wires together to simulate have a switch.
Does the car start operating as you wish? If so, then you can buy a simple low-cost "SPST" 2-terminal on-off switch for a couple bucks. And you wouldn't need to mess with the DPDT or similar more complicated switches.
