I want to be able to modify the scrolling/middle click behavior for individual apps on Windows 7, so that the scroll to zoom direction is always consistent across apps. This script makes the middle button act as a hand tool in Adobe Acrobat, for instance:

; Hand tool with middle button in Adobe Reader
#IfWinActive ahk_class AdobeAcrobat
Mbutton::
#IfWinActive ahk_class AcrobatSDIWindow
Mbutton::
Send {Space down}{LButton down}  ; Hold down the left mouse button.
KeyWait Mbutton  ; Wait for the user to release the middle button.
Send {LButton up}{Space up}  ; Release the left mouse button.
return
#IfWinActive

(It would be great if this could be adapted to allow "throwing" the document, too, like in Android or iPhone interfaces, but I don't know if it's possible to control scrolling that precisely)

How do I invert the scroll wheel-->zoom direction?