If you’re using a non-custom KoBoToolbox server, the idea of using a dynamic external data file will not work.
Feature requests could go here: https://github.com/enketo/enketo-express/
I’ve already created it for you: https://github.com/enketo/enketo-express/issues/228 (but note that we’d still need somebody to contribute this feature as I probably won’t do it myself soon).
P.S. Enketo is using # fragment identifiers for something else, i.e. to go directly to a specific question.
