[Brian]

Okay, after a bit of experementation, this appears to work, with the caveat that you need to select something in the sidebar manually before running it. Hope this helps!

activate application "OmniFocus"
tell application "System Events"
	tell process "OmniFocus"
		--select all
		keystroke "a" using {command down}
		
		-- expand all
		tell menu item 1 of menu of menu item 15 of menu 4 of menu bar 1
			click
		end tell
	end tell
end tell