@sethvargo that goes against bundler practices which is unfortunately one of the things I try to stay keen on.  Additionally that makes CI pretty worrysome (to me).  Our CI instance currently has an vanilla ruby install from mainline (ubuntu 12.04) on it with just Bundler.  Being able to quickly clone and get it into the agent to run without having to do any fuzzy patching or replacing the Gemfile ( I am likely the odd ball thinking that you should never replace the Gemfile in an automated scenario,  Patching, or modifying, but it's better to accept the defaults and get to where you need to be.

P.S. Yes I have run CI without bundler and I the support of it was the labor intensive.