Have caught a few sole and flounders and all on either fly or crayfish bait except one huge yellowbelly flounder on a handline using gravy beef for bait when I was a kid. You will be amazed how well a decent yellowbelly flounder can pull on a light (or fly) rod.
I need to finds a spot where there are planty to try out a few new ideas on them.
In the tropics they are pretty easy fare on fly using crazy charlie flies. At an Island called Tarawa I caught twenty one afternoon.