I've tested this with AIR29 and it does work. It is only supported when targeting a bundle, not native or the default air.
This means what adt produces is a folder containing your built project, as opposed to a single EXE or AIR file.
You'll need to put this in your application.xml, just below the
-target bundle in your adt command. If you're using FlashDevelop , you do that by editing Packager.bat. Find the line starting with
call adt... and modify it to this:
call adt -package %OPTIONS% %SIGNING_OPTIONS% -target bundle %OUTPUT% %APP_XML% %FILE_OR_DIR%