The first prize options look like the most balanced and useful
without having to add what might be a major update to do it (ie a
whole new store. The beach was a MAJOR update, and the stores were
likely a massive reason for that), the only alternative I can
suggest is that instead of putting a symbol on the Pokémon that won
the strongest Pokémon rally is that the winner gets a Retro Kanto
starter voucher or something. Something that's typically locked
behind premium, and thus has value and it could be claimed from
Rowan or something after he says something like "that was
impressive, why don't you take this as proof that you're a capable
trainer" or something.
Just remember: You can't prove God didn't crawl out of the ocean.