There have been accidental local catches of flounder and sole on all manner of baits over the years. Just last weekend one was caught during the Moki 1000 on a small piece of mussel.

I think all sorts of shellfish baits would be worth a try.
The biggest issue with that, here in Napier, would be the crabs decimating your bait before any flounder came by.
But seeing as I have the next two weeks off work, I will be putting in some hours to try and crack it