Like I said, in SAFE the idea is to allow for public addresses/transactions as well.
Here it is 
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So you can become part of a group, you can show that group a “used once” public address and you can also say to that group: “This is my public address with 4 Safecoin in it”. And then that group could verify that and request you give up ownership. If you do within the next few seconds they reach consensus on the fact that you indeed burned some tokens. No need to change any consensus algo.