Install the pre-release of bundler. When 1.0 is final the --pre flag will not be necessary.
$ gem install bundler --version=1.0.0.rc.2 Successfully installed bundler-1.0.0.rc.2 1 gem installed
Modify your Gemfile, and locally re-bundle you app with the new bundler options. If bundler complains about the Gemfile format, fix it according to the directions on http://gembundler.com/v1.0/index.html. If you have an old bundler gem defined in your Gemfile, make sure to un-pin it from 0.9.x.
$ echo >> Gemfile
$ bundle install --path vendor/bundle