why cant you just use the menu button?
im not sure exactly how to do it but heres how to do it with apple script
-- This script creates an ad-hoc network with a password and changes your
-- network location.
--
-- I just added network passwords and network locations to a script which
-- comes from StefanK:
--
MacScripter / creating ad-hoc airport network from script
-- Set NetworkName to be the name of the wireless network you wish
-- to create. This will also attempt to set the network location
-- to that name as well.
-- Set NetworkPassword to be your wireless network password. It MUST BE
-- 13 characters long (or 26 hex digits).
property NetworkName : "MyAdHocNetwork"
property NetworkPassword : "thirteenchars"
property CreateMenuName : "Create Network…"
try
do shell script "/usr/sbin/scselect " & NetworkName
delay 2
end try
tell application "System Events"
tell process "SystemUIServer"
tell menu bar 1
set menu_extras to value of attribute "A

escription" of menu bar items
repeat with the_menu from 1 to the count of menu_extras
if item the_menu of menu_extras is "Airport Menu Extra" then exit repeat
end repeat
tell menu bar item the_menu
perform action "AXPress"
delay 0.2
perform action "AXPress" of menu item CreateMenuName of menu 1
end tell
end tell
repeat until exists window 1
delay 0.5
end repeat
tell window 1
keystroke NetworkName
click checkbox 1
keystroke NetworkPassword
keystroke tab
keystroke NetworkPassword
click pop up button 2
click menu item 2 of menu 1 of pop up button 2
delay 0.5
click button 1
end tell
end tell
end tell