Similarly, I've wondered how much impact could be had by changing Facebook's charity donation prompts to EA-recommended charities.
EDIT: Just realised you said "only for its reputation", which makes my arguments for Apple less relevant (though it is still a very highly-regarded brand!).
If money is no object, I'd say Apple. It's one of the most loved brands, it is phenomenally good at marketing and it holds enormous financial influence. Not only could you direct a portion of its revenue to EA causes, you could also do things to encourage the spread of EA — for instance, add a "round up" feature to Apple Pay that rounded all your purchases to the nearest dollar, with the money going to EA funds.
Obviously this is not at all possible, but it's an interesting question to think about. Even if no one can "buy" Apple, it's perfectly possible for an EA to eventually become CEO of Apple and that could have much of the same impact.
This is a really good idea. Even better might be to commission him to make a documentary with a very EA-focused take on animal welfare. It's hard to say how much his explicitly climate change focused documentaries have done, but anecdotally it feels like they've been influential.