You can do that for quick access to your pen pressure utility to adjust your pen pressure on the fly. 

First, you will want to open the Xencelabs Settings panel. 

[1] Select your Quick Keys from the left navigation column.

[2] Select the application you want to set the pen pressure utility to open.

[3] Select the button you want to assign it to and click it.

[4] Select Tablet/Display.

[5] Adjust Pressure.

Now, when you are running that application, you will notice the name for button three will be displayed as Adjust Pressure.

Now, when you press that button, the pen pressure utility will be displayed for easy access.