Unfortunately Simple address is only working for pages in EPiServer database.

The suggested work around would be to hook up to event EPiServer.Global.UrlRewriteProvider.ConvertingToInternal

and in the event handler make a call to some own implemented method on your PageProvider with the Url (or the segments for the url). If the page provider recognies the urlsegment it should set the UrlInternal (on format like /templates/Page.aspx?id=4__providerKey&epslanguage=en) on the event argument and mark the argument with IsModified (to prevent further rewriting processing).