It's a bit of a Catch-22. Work around it by:
Make a app (or script) post for your app (or script).
Also tag it with placeholder.
And put "PLACEHOLDER -" at the beginning of the title.
Also, indicate in the post text that the app is not yet ready for prime time.
This has already been done a few times, for example:
"Chatdump - a site monitor (placeholder)"...
I like the idea of adding a close reason for this. A custom off-topic reason, something like,
This is a placeholder question for an app that's still under development; it will be deleted within 9 days unless regularly edited to show progress on development. If the app is ready for others to use, follow the template and flag for moderator attention to ...