I think it might be a good idea to fake a global apocalypse to send all the billionaires scrambling to their bunkers and then just go ahead block the doors with a big rock.
a lot of them are volcanic so you can keep building higher up the hillside as the water rises. the sea's not gonna rise 50m, and you can easily get that much height on the volcanic ones.
Oh okay. I think I was thinking of the Maldives or similar types of completely flat islands. As far as I know, global warming isn't making a catastrophic volcanic eruption more or less likely on those islands, so I guess their plans are slightly smarter than I first credited.