I liked this second alternative. Have you ever used it?
But I need the forked coin wallet for that, right? I will not receive bitcoin, but the forked coin.
BTCD.io has a list of wallets that support BitcoinDiamond. I've never heard about most of them except for Atomic wallet, Bitpie, and Mobi. If you're not comfortable storing your funds in closed source wallets, you could use a reputable exchange instead but a personal wallet is always a better solution.
As for the service, I gave you, it's very reputable so If you're fine with the fees they're taking, I highly suggest it. You could also check their bitcointalk thread to see what people think about it.