As an immediate solution, we will let our custodians provide PoR and PoC on a daily basis and we will syndicate this data on our site. We are looking at
http://www.bullionvault.com/audit.do that appears to have solve the daily auditing-report problem, but it still not the provably-at-a-distance-true that you're asking.
I'd recommend Mike Maloney's
GoldSilver or
Gold Bullion International.
These are great companies. Thank you and we will reach out to them tomorrow as we build a matrix of these vendors with whom we can work.
You might put James Turk, founder of GoldMoney.com, into the mix. He had been quite skeptical of Bitcoin, but more than a year ago, after doing a lot of his own research, he embraced cryptocurrencies and had been trying to use them at GoldMoney.com. I don't know exactly how, though. He's very critical of the entrenched powers and their abuse of the gold market in order to support fiat currencies. So he not only has a great deal of knowledge and experience about the gold and other precious metals markets, he is very interested in how cryptocurrencies can disrupt the destructive and corrupt politico-economic systems in place now.
I have no idea how to get his attention. I am sure that wealthy, influential people like him are bombarded with "great ideas" all the time by naive entrepreneurs. But if you make a solid business proposal (and it sounds like you have a very solid beginning), he might listen.
Google "James Turk Bitcoin" and you'll find a few links, including this interview (
http://bitcoinmoney.com/post/31942156510/james-turk-felix-moreno). He's been trying to integrate Bitcoin into his business, but I'm not sure how successful he's been. (And I haven't done all that much research.) It would be easy-ish to take payments in bitcoin (several companies are already doing it), but what you're proposing is far more advanced and interesting.