Using Dell middle trackpad button as middle mouse button?

I have one of the various Dell laptops that actually has 5 buttons around the trackpad (a Latitude E5550):

I really like the middle mouse button and use it quite often, so I would like to use the middle button above the trackpad as a middle mouse button. However, I can't find any way to do it. Its default function is to allow scrolling with the nipple when held down, but I never use that functionality so I don't care about that. Also, I'm aware of the "middle click emulation" by holding left and right buttons down at the same time, but it's not really what I want.

I want to be able to map pressing the middle button to a middle click, simple as that. Using the latest version of the Dell "touchpad properties" software, I look through its interface and I don't see anywhere I can customize the functionality of that middle button. So is there a way to do it?

There it is in the Dell Pointing Devices software. The version is dated Feb. 19, 2015, Windows 8.1 64-bit.

NOTE: this is not particularly clear in the Dell Pointing Devices software, but you first have to click on the "Pointstick" image along the top before you will get the option to change the behaviour of the middle button above the touchpad (the two buttons below the touchpad are considered part of the touchpad). Even though it is physically close to the touchpad, the middle button above is not considered "part" of the touchpad; it is considered "part" of the Pointstick, so the option to configure that middle button above the touchpad is in the Pointstick settings. So first click on the Pointstick image along the top, then click Buttons, then you will see the "Middle Button" option.

^{(Click image to enlarge)  Source: NotebookCheck.net}