I'll have the initial master wallet with a bit less than 21 000 000 QBC. We can split that up into 5 different wallets, encrypted, backed up to two forms of physical media. A bank in Montréal acts as a trusted third party and doesn't allow access to the vault before a certain moment in time. Fool proof method + the fact that I actually would never dream of touching the premine for illegitimate reasons should be good enough for anyone.
It would be better that we have zero premine. When the coin is launched and mined, a percentage of the coins will be sent to the 5 different wallets you mentioned. As the distribution, payment to development are long term processes, not a large amount of coins are required on day 1.
Not all the premined coins will be lost in one go if the wallets are breached. This will also prevent a large dump of coins soon after the launch by the claimant. If there is not enough mined coins, then the claimants will have to wait for the coins to be available.
The slow release of the coins is beneficial to the long term health of the coin.
However, this process will give the developers less control of the coins, they may not like it.
If you read through this thread you'll see that a slow release is exactly what's planned. I'm the dev and I have no problem with giving up control of the premined coins so that they can't be spent or stolen. I'm the first one who suggested it actually. The coins will stored in a bank vault and not touched until the first airdrop period. QBC will stay rare and valuable except for a few smaller scale giveaways as a promotional tools. The premine is here to stay though as I intend that most of the coins actually stay within Québec, for Québecers.
edit: Also I think you were suggesting taking a percentage from miners instead of a premine but that's really equivalent to having a premine anyway but with way more complications.