I use Roth's "Panther Wallet" I don't think you can get them anymore, but it uses a 3M filter, meaning that you can get a peek with the wallet closed and they can't see a thing.
It's a leather biz card case, so I take it out, have them write on in, and have them place it face down back into the wallet as I hold it - So no one can get to it and I can't secretly see what they've written.
I then place it in their hands and move on from there.
I think that canceling the idea of a peek while getting your peek is a nice way to eliminate it from their minds - I try to literally get the peek as I say those words.
This approach really only applies to wallets you can peek without re-opening it, but for wallets like that, i.e. assassin or the Becker wallet (can't remember it's name!) you could have the card placed back in the wallet for the same reason, so you CAN'T secretly get a peek, then re-open, get your peek while grabbing another biz card out to dupe the word on, or as Becker suggests, have an elastic band in your wallet to wrap around it, so there's NO WAY you could secretly get in...
I'm sure there's other ways to approach this, but that's the way I do it
Best,
DC