At this specific bridge (not sure if you missed the discussion) there is a parapet extension over the Down Hertford Loop but not over the 4 ECML tracks. https://www.google.com/maps/@51.889...4!1sD-EiLYeofg1M1aQ-7jT6mQ!2e0!7i16384!8i8192
Ah yes, I see. That said, even the unextended section seems pretty hefty (up to the young man's neck). You'd have to be pretty determined to dangle anything over that.