Those errors usually mean websockets are not proxied correctly, make sure your nginx setup is correct. If you are using cloudflare you need to disable acceleration. They don't support websockets on smaller plans.
@Tanner write API could help with that, but until then, here's the high-level implementation/workaround:
FTPP (form-to-post plugin) establishes new POST route at /feedback
When that route is called, take req.body.text (where text is the id in the corresponding form) and call Topic.post as a pre-registered user.
That's pretty much it. There's more to expand on (such as spam prevention/throttling/auth/security), but yeah.