I looked at this stuff
they all use:

 
    def button_press(self, widget, event):
        if event.button == 1:
 

and one click opens the menu.

for me - with the same code - only doubleklick works.
I found that a normal launcher also work, but only with doubleclick.

I don't know if anyone is still interested in this, but I found a sort of solution. I did exactly as michote, editing the showdesktop applet. The problem is that you need a short delay before sending the keystroke to open the menu. I set it as 0.1 seconds. I also made the cursor move to the corner of the icon and back again, so the menu opens in the same place every time. I set the vertical offset to 46 since my awn bar is 48 high, this means it just sits on top of the bar. You also need xsendkeys installed, which can be found in the lineakd package. To test it out, replace the showdesktop.py in /usr/share/avant-window-navigator/applets/showdesktop with the following, and then add the Show Desktop applet to your awn panel.

 
  


  
#!/usr/bin/python
  


  
import pygtk
pygtk.require('2.0')
import gtk
import time
import subprocess
import awn
from awn.extras import awnlib
awn.check_dependencies(globals(), wnck=['xfce4.netk', 'wnck'])
import Xlib
from Xlib import X, display
  


  
the_display = display.Display()
the_screen = the_display.screen()
root = the_screen.root
  


  
applet_name = "Gnome Main Menu"
applet_version = "0.1"
applet_description = "An applet to pop up the gnome main menu."
  


  
# Applet's themed icon, also shown in the GTK About dialog
applet_logo = "start-here"
  


  
class ShowDesktopApplet:
  


  
    """An applet to pop up the gnome main menu.
  


  
    """
  


  
    def __init__(self, applet):
        self.applet = applet
        applet.title.set("Main Menu")
        applet.connect("button-press-event", self.button_press)
  


  
    def button_press(self, widget, event):
        if event.button == 1:
            the_focus = the_display.get_input_focus()
  


  
            #move pointer to icon corner
            x_corner = event.x_root - event.x
            y_corner = event.y_root - event.y + 46
            root.warp_pointer(x_corner,y_corner)
            the_display.sync()
    
            #display menu
            time.sleep(0.1)
            subprocess.call(["xsendkeys","Alt_L+F1"])
            time.sleep(0.1)
  


  
            #move pointer back to original position
            root.warp_pointer(event.x_root,event.y_root)
            the_display.sync()
  


  

if __name__ == "__main__":
    awnlib.init_start(ShowDesktopApplet, {"name": applet_name,
        "short": "gnome-main-menu",
        "version": applet_version,
        "description": applet_description,
        "theme": applet_logo,
        "author": "987poiuytrewq",
        "copyright-year": 2009,
        "authors": ["987poiuytrewq"]})