That may be impossible - it depends how far back the problem goes: If someone stole some money three weeks ago and spent it, then any transaction descending from that original bad transaction would have to be invalidated too. This could conceivably be a large fraction of all bitcoin transactions since then because of the way bitcoins get 'mixed'.

In other words, most likely we would have to reset everything to the way it was before any of the bad transactions, and they might have started years ago (my impression is it was a small but long-term drain). This would be insupportable to anyone who has sold any goods since then.

Also, you don't need to persuade the miners, so much as the sellers (of goods): The miners will mine whichever blockchain on which bitcoins have value, and bitcoins have value only because people accept payment using them. In other words, your main challenge is to convince anyone selling goods in bitoin to update to the new client - the very people who would likely get screwed by reversing transactions.