I have quite a few open source projects that I wish to build/release automatically on pushes/tags. For the release, I need the same environment variables (passwords and API keys) in all of my builds. Unfortunately, Travis currently only allows setting them per project. This quickly becomes annoying, especially if you ever have to change a password.
I worked around this by having a seed job where I configure these variables. That job then uses the Travis Ruby-API to push those variables to all other of my build jobs. Feel free to fork the repo and adjust the code to your own needs.