bundler 1.0.0.rc.2 not working with rails3 and jruby 1.5.1

I can't get a multiplatform bundler Gemfile to work in JRuby with a simple raisl3 app.

See: http://github.com/carlhuda/bundler/issues/issue/502/#comment_336670 for more details.

The only way to start the rails app in jruby seems to be to comment out the platform-specific parts for other Ruby VMs.