Run on Heroku using 'npm start'

I’m currently trying to deploy my Meteor application to Heroku and want it to run using ‘npm start’. I’ve defined a script in my package.json file that starts Meteor up with some settings. This all works locally, but I can’t figure out how to do this on Heroku. I’m using this buildpack: https://github.com/matb33/heroku-buildpack-nodejs.git.

Any help would be appreciated. Thanks!