Some middle languages, such as `Stylus`, provides two ways to be compiled: through `connect` middleware or through CLI tool. The later can generate static compiled assets(i.e. `.css` files).

So I want to use middleware on development mode but static assets on production. I know that I can use `app.configure('developmen'...)` to ask `express` (not) to use some middlewares on development mode. 

On an IaaS enviroment, like Amazon EC2, I can run a simple shell script to automatically re-compile all my assets. But how about PaaS, specifically Heroku? How can I tell it where my `.styl` are and where the `.css` should be generated?