Automator workflow and Calendar events: getting information into the workflow from Calendar?

I would like to create an Automator workflow calendar event so that when events are due in Calendar, the action will create a task item in Things3. Since Things3 is scriptable, it is easy enough to use the Things3 URL scheme to accomplish this.

The thing is, it would be ideal to have one such workflow that creates tasks for a variety of calendar events. That would mean the workflow would have to know what event triggered it to run.

As far as I can tell, however, there is no input passed from Calendar run it runs a program (via the “open file” alert), so as far as I can tell there is no reasonable way to do this (at least not efficiently; the workflow could use Calendar scripting to figure out what event occurred within the past minute or two and had an alert that matched the running program, but that just seems ridiculous).

Anyone know something that I am missing here?