Here is a repo that has the button included: https://github.com/southpolesteve/lucre
Obviously I never really promoted it and I'm glad to see that Heroku built something official. But maybe someone far in the future will see this comment and remember :)
Quick edit: Here is the announcement email to the local railer's group https://groups.google.com/forum/#!topic/Mad-Railers/-1MkbbkX... To be clear, I have no reason to believe that Heroku used anything I made. Just wanted to self promote a bit.