Dynamically creating subdomains on Heroku with nodeJS?

node.js heroku express subdomain

Yes. You can indeed dynamically add domains to your Heroku app using the Heroku Platform API. Here's a link to the exact bit you need: https://devcenter.heroku.com/articles/platform-api-reference#domain

You can then read in the domain data via the node request object (req.url, I believe).