Create a handler that is restricted to admins only. When that handler is invoked with a simple GET request you could have it check to see if the seed data exists and if it doesn't, insert it.
Configuring a handler to require login or administrator status.
Another option is to write a Python script that utilizes the Remote API. This would allow you to access local data sources such as a CSV file or a locally hosted database and wouldn't require you to create a potentially unwieldy handler.
Read about the Remote API in the docs.