That can be done too, but you have to specify another device most surelly. The evtouch driver, last time I tried does not support buttons from other accesories, in my case with the wacom driver I had to modify the N-TRig device to look like this:
Identifier "Wacom N-Trig class"
MatchProduct "HID 1b96:0001|N-Trig Pen|N-Trig DuoSense"
Option “Button2” "3"
Obviously the Driver wont be Wacom for the V. and the HID ID will be different.