Just deposit your coins into your hardware wallet and you'll be too lazy to withdraw them. That's for real and that's been effective to me as I don't want to withdraw my coins in my HW whether just to sell, trade or even gamble.
Because that's going to give some bit of effort in withdrawing it and you have to connect the HW to your computer and do the necessary process. I think this is way better than staking to a wallet.
The latter is just the same as putting your money in the bank through time deposit.
Not sure if this will even applicable to addicted gamblers mate, self exclusions mostly comes from those who cannot manage their gambling activities meaning either they are hooked or already addicted and has nowhere to go but to exclude themselves .
so what you are sharing will only effective in short time because for sure as long as they knew there are funds available in their hardware wallets? for sure they will use them to gamble in any ways.
that is sad reality here mate.