Amusingly enough, the "Many Paths to (one of) the Gods" section in the Codex, which contains advice on how to realize a given character concept(Storm Lord of Hurrian) through a variety of different builds, has one example where a player does the
exact thing that SamhainIA mentions in his opening post.
Codex, p39 wrote:
Jimmy has elected to create an Arcane Archetype Hero; because everyone that knows Jimmy knows he is going to play a wizard. This is an unusual choice because a human character with the Arcane Spellcasting Talent has absolutely no option to become a full-fledged Divine Spellcaster as well. Heedless of these constraints, Jimmy creates an Eldritch Caster and, keeping to concept, selects anything that relates to electricity.
Jimmy begins as a proud son of a landed family and selects the Noble Born Background. Like Nelson, Jimmy cannot move directly into the Holy Champion Path, but he does not want to anyhow. Instead, he joins the church with his Tier I advancement by, selecting Initiate Iterant; this has the additional benefit of teaching him a single divine spell chosen from a small number of traditions.
During Tier II Jimmy becomes an Anointed Priest of Hurrian which leaves him free to join the Storm Lords during Tier III. He also intends to use the Learn Spell Talent to expand his Hero’s repertoire of Divine Spells.
Probably also needs a note in the errata that you can't actually do this then.