What we could do (besides taxing it away) is configure a limit to what they are allowed to do with it.
I also see room for special titles with cosmetic privileges if someone accomplishes to pay the enormous tax.
It will be hard to find the right privileges. Something like a medal or an outfit is obviously doable. An annual fancy dinner for the group doesn't seem over the top. A daily 30 min slot on the TV for them to bid on exclusively, or each their own slot annually. Can grant 3 lectures in any university. It gets slightly dubious if we add special construction permits for locations no one else may build in.
The funniest I could think of, at 10 bl+ we seize all of your money and assets, you are forbidden to participate in the financial system. You get a robe and a cloak and a card with which you can eat any place, stay at any hotel, buy cloths, do shopping, take a taxi and take any flight with a maximum of 3 guests + partner and kids.