You're only adding 3 lines of code in this example.
In package.js (inside the Npm.depends)
'babel-preset-stage-0': '6.5.0'
In babel.js (top of file)
const stage0Preset = Npm.require("babel-preset-stage-0")
In babel.js (inside getDefaultOptions function)
options.presets.push(stage0Preset)