East Coast will also sell me an Emerson Park - Hereford Route +Any Permitted Super Off-Peak Return (£70) via Upminster and Birmingham New Street. Since Upminster is a valid interchange station for your cross-London transfer and there is no break of journey restriction, you can legitimately start short at Upminster and use London Underground services all the way if you prefer to get to Euston. You can also finish short at Ledbury.
To obtain the desired itinerary, go to eastcoast.co.uk and enter From Emerson Park To Hereford Via Birmingham New Street. Click Timetables only. Once the itineraries are up, specify Trains which call at Upminster and click Update. Once updated itineraries are up, click Buy a ticket. You should be shown hourly journeys going via Upminster, and then c2c to Fenchurch Street, and onwards via Euston and Birmingham New Street.(I used Saturday 8th Feb as an example.) This for some reason does not appear to work with Ledbury as the destination but Hereford is the same price anyway.
