- Download and install Platypus (http://www.sveinbjorn.org/platypus).
- From Platypus->Preferences, install the command line tool.
- echo "4.5-beta" >VERSION
- make
- Download the most recent xar and libarchive source from opensource.apple.com.
- Use the instructions here: http://www.timdoug.com/log/2010/08/25/ to build fat binaries.
- For libarchive, make sure to add "--enable-bsdcpio --disable-bsdtar" to the config line.