Zoom with Mouse wheel in Design Entry CIS v.16

How can I use mouse wheel to zoom in(forward) and out(backward) in version 16 of SPB, in Design Entry CIS?

I tried to put this for example:

set buttonfactor = 1

button wheel_up "zoom in $buttonfactor"
button wheel_down "zoom out $buttonfactor"
button Cwheel_up "zoom in $buttonfactor"
button Cwheel_down "zoom out $buttonfactor"

in the "env" file in the directory directed by HOME variable in Windows. But it doesnt help, anyone can tell me what has to be done to make it happen? thanks