I use two services, GitHub and Heroku. I have set up remotes for each of the repositories online. However, I want one file to be pushed to Heroku, but not pushed to GitHub. Is there an easy way to do this without having to edit .gitignore every time I push to a different service?
Like VonC said, it's not natively supported to do what you're asking.
I think the best way to do this would be to have different branches.
For example, you would have your master branch, a github branch, and a heroku branch.
Anything that is synonymous between the two branches would be located in master, and anything specific to github or heroku would be in their respective branches.