I created a small ruby script which will package for the two supported sizes. For each size it will remove any directory named after the wrong size, and files named after the wrong size. You can also pass in an ignore file which has a list of assets to remove before zipping the file.
It will read the widget.xml file as well to get the right widget name.
Run packager.rb -h to get the list of options.
Widget PackagerIts AS IS software but you can create issues on the github page.