Unfortunately, [I tried to do this already](https://github.com/seattlerb/seattlerb.org/pull/42/files) and [Ryan had to revert](https://github.com/seattlerb/seattlerb.org/commit/0e6494fabb9f2218038a429059e7e2ffb39914ad) because Bamboo is using such an old version of bundler that it doesn't allow specifying the ruby version.