This is Mikey with Airship Technical Support. My apologies for the delayed reply to your question. As you have observed, there isn't a way to support this behavior without extending the service worker. We also don't provide any support for doing so at this time. That being said, this is something that would be great to have the ability to facilitate, and so I have put in a product enhancement request on your behalf.
Thanks for your question, while I don't have any timeline for such a request to be implemented it is something that we will be looking into.
Please let me know if you have any follow up questions that I can answer for you regarding this.
Airship | Technical Support Engineer | Portland, OR