Hi Chad, thanks for giving it a thorough investigation.
I think the solution might be changing the http headers to include
Service-Worker-Allowed: /
as described in:
Increase scope of service worker via HTTP-Header
or I was thinking if using the routing module and make it pretend all forms should open in the _/theme/ directory. I tried looking into the documentation but I have no idea if the routing makes the browser believe the page is actually within a different directory. 