media_url helpers are plain old route helpers defined by the Dragonfly custom endpoint.
It would be helpful if these helpers used the
config.asset_host if present, in the same way Rails’ native
asset_url helpers do.
The easiest solution would be to override the route helpers with a helper module included in both PushType and the host app. I’ve successfully done this in one our project sites so just need to merge the work in to PushType core and add a few tests.