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 ...
Is your app listed here? If so, you should edit its entry and paste the URL to this question in the field Stack Apps Post (optional). If you don't have any apps there, you need to create one first and add the question later.