I hope I understand the question correctly but you can also pre-populate the text in the text field in the incoming JSON. By default, that'd be user_input, but you can also customise the ID via the field_id setting on the block. So if you feed in data with "user_inpit": "Some text here", the field will get pre-populated.
Couldn't you do something like this and define alternative routes for all the endpoints?
In general, Prodigy should support custom path-based routing because all requests are made using the releative paths.