Technically such an agreement would be in violation of the CBA, could anyone prove it. Technically.
But there's no reason the situation has to be structured identically. It's certainly possible he'd agree to the one year overpayment without the same sort of non assurance assurances we gave to KK. Remember, he'd still be an RFA and the outcome for him if we don't want to keep him is he becomes a UFA a couple years early. But it's two seasons before he's anything but a trade target.
As for RFA shenanigans more broadly, somebody really should go after Shane Pinto. 20G scorer, and Ottawa is in a cap jam and trying to sign him for an utter joke of a $1M contract. He wants $2.5 and is easily worth it. Up to $4.29m is only a 2nd. Sign him for a 1y, $3.5m contract, Ottawa probably can't match. We don't have the cap space with our overloaded D, but that situation is just ripe for the picking. If I'm, say, Detroit, I'm all over that. And even if they do match they have to move a player out at a huge discount to get under the cap.