Set a keyboard shortcut to clear all tracks from the Up Next queue in iTunes
This following script will work on OSX &lt; 10.7. 

activate application "iTunes"
tell application "System Events"
    tell process "iTunes"
        click (first button of scroll area 1 of window "iTunes" whose description is "up next")
        delay 1
        click button "Clear" of UI element 1 of row 1 of table 1 of scroll area 1 of window 1
    end tell
end tell