What if we post a real time list of customers accounts(notified by a different number) and the customers can check if the amount associated with their account is being displayed correctly or not and then match the totals of the held funds with the total amount of bitcoins held. Ofcourse the summary will be available in a small table format where as the customer list and address will be in two different pages. This will be 100% realtime.
This will be in addition to the external audit. Is this sufficient?
You won't be able to minimize fees across your wallet base though with this plan, costing you (meaning your users, since you'd have to pass that cost onto them, meaning theoretically fewer users) a hell of a lot more over time. Normally, you'd write a script to pull from the addresses with the highest (or sufficient) balance to minimize fees in order to be able to maintain a constant or low variable fee for withdrawals - the same way that Coinbase allocates different buy/sell prices for buys/sells with more sig figs. This is why on exchanges such as Havelock, if you check your deposit address, it won't show your actual account balance, which is maintained by the server's ledger rather than the blockchain (off-chain).
The 1-satoshi+signatures would only cost you a hold (not a spend) on X number of satoshis, where X is whatever number of addresses your model would validate per day. With that type of model, you could probably validate each address once a week, so if you had 70,000 customer addresses total, you'd only have to put a hold on 10,000 satoshi per day.
Keep in mind that in order to use the 1 satoshi solvency method, you'd have to create a wallet backup before executing an iteration of the verification run to restore the broadcast satoshis back to your wallet after the 1-day period of viewing has passed (otherwise they'd be effectively lost or at the very best, extremely hard to recover). Also - your auditor team could write a code to monitor the BTC flowing in and out of your company's set of customer addresses to provide realtime aggregate cashflows for your financials - this would be the mechanism that would enable users to ensure they'd be able to withdraw on any given day.
