[jruby-user] dealing with .ruby-version file

I have a project which I want to test with jruby.  I created a jruby fork
of the project and started hacking away the gemfile and other stuff but of
course changing the .ruby-version file always causes a conflict with the
master branch.

I am wondering if anybody has a cool trick to set up the .ruby-version
based on the git branch or something like that.