OpenAI isn't offering a viable product as it currently stands. This is why we only saw toy usage with the Plugins API and now with tools as part of GPTs. Since OpenAI wants to own the front end of the GPTs there isn't any way to implement the parts which aren't there.

About non-blocking: I am asking for their tools API to not block the user from continuing the conversation while my tool works. You seem to be thinking about something else.