So…there is fledging support for XMLTV in there (just one of several little easter eggs). I’ll leave you this slightly mysterious HTTP endpoint. The lineup encodes the path to the XMLTV file, as well as the title of the lineup.
Without a DVR setup, issue this request:
POST http://localhost:32400/livetv/dvrs?device=device%3A%2F%2Ftv.plex.grabbers.hdhomerun%2F123032B8&lineup=lineup%3A%2F%2Ftv.plex.providers.epg.xmltv%2FUsers%2Felan%2FDownloads%2Ffreeview.xml%23Freeview&language=eng
Let us know how it works; I only really tested with a single file, but it should be easy to tweak 
