Execute a program by double-clicking the taskbar and/or the desktop, Windows 7

An AutoHotkey script can convert double-click on the taskbar to click. In fact, with AutoHotkey you can do anything you like with any mouse/keyboard event.

The article Single click vs Double click on tray icon contains this script that you can adapt to your needs, by ignoring the second click of the double-click:

#Persistent
Menu, Tray, Add, TEST, TEST
Menu, Tray,Default, TEST
Menu, Tray, Click, 1
Return

TEST:
If x = 5 ;here you can set how many clicks user can do max
    Return
x++
SetTimer, Run, 300 ;here you need to experiment to suit you
SetTimer, DEL, 350
Return

Run:
SetTimer, Run, Off
MsgBox % x
Return


DEL:
SetTimer, DEL, Off
x=
Return