how to listen on any port on heroku when a web port 80 is already in use?

I am new to heroku and i have deployed a meteorjs application on heroku. My Meteorjs application is a webapplication, so after the build is done it runs on heroku on port 80. But simultaneously i also want to listen on a port eg:4000 or any so that i can catch my webhook events fired by any third party i want to listen to. On my local machine it runs perfectly with webapp running on a port and listener running on another, but on heroku after i deploy its just the webapp which runs and listener doesn't listen. Can anybody help me or guide me. Any new solutions are also welcome..

via Chetan