If you are concerned about lowering the ABV, you may want to mix some campden tablets in there to kill of the yeast, so that when you add some fruit it won't get fermented (though the yeast may not be able to tolerate much more than 14-15% anyway).
Can someone back me up on that, or explain more?
As for delicious summer flavors... blueberry? Blackberry? Something like that.
PS- Is it finished fermenting?