Basically, you're in trouble. Any finish you apply will have to stand up to near-boiling water, and expansion and contraction of the basin surface with changes in temperature. Not many surface applications are going to take this punishment. The only sure way would be to have the manufacturers re-surface the sink - which would probably end up costing more than a new one, even if they agreed to to it.
But then what's going to stop the problem arising again?
Personally, I'd probably curse a bit, cut my losses, and go for a ceramic replacement.