I figured out how to use Ruby to push Growl notifications. I would still like to find a JavaScript solution, but if there is no way to use JavaScript, then here is a Ruby solution:
Use the ruby-growl
gem:
gem install ruby-growl
Then in your Ruby script:
require 'ruby-growl'
g = Growl.new "localhost", "ruby-growl", ["ruby-growl Notification"]
g.notify "ruby-growl Notification", "It Came From Ruby-Growl", "Greetings!"
Also, in order for this to work, you have to enable "Listen for incoming notifications" and "Allow remote application registration" on the Network tab of the Growl Preference Pane