While you're waiting for Khoros I think you have the right idea already until they provide a better alternative. I have added event listeners to the submit button without any issues.
However, I don't know of a way to get the id of the post at that point since it doesn't really exist yet. So, I think you might want to grab the info on your own like you suggested in number 2 above directly from the post page.
Then you would need to use http.client.request (khoros.com) to make an external API call to send out your info.
