Have been around that area a few times.
There are a few spots (some hard to find) on the Banana River near the causeway. Great flat water if the wind is right. I discovered them by seeing kites in the air.
There are a lot of local kiters around. If the wind is blowing - you'll see them. There is a big Windsurfing launch (and kites) on Merrit Island just off the causeway, you can get some local info there.
Check out the this link: http://www.calema.com/