Is it possible to add a toolbar button to invoke a, say, Automate plugin? It would be preferrable if a user can call the plugin with a single click, instead of having to go 'File-> Automate-> plugin_name'.
I am not sure about toolbar but you can add button to panel that will activate plugin using java script, providing that your plugin is scripting aware.
Use script listener to see how to call your plugin from java script, design a panel in Adobe configurator (or any other way - flash html5) add button to panel, and activate script on button click.
Retrieving data ...