On Sunday I added three pounds of thawed blueberries to the secondary and racked my American Wheat on top of it. I pureed the berries in the blender then put them in a pot and heated them to 160-170 for about 15 min to kill off any bacteria. The fermentation kicked off good from all the sugars in the berries but it is slowing down now. I'm hoping it will turn out good.
I have been reading "Designing Great Beers" and the section on fruit beers says that many of the brews that made it to the second round during the National Homebrew Competition used extract. You could probably make a good fruit beer using wheat DME and a bittering hop. Then add the fruit of choice to the secondary. Among the second round beers cited in the book the most common fruit used was raspberries. There were a few second-round beers that used blackberries, cherries, passion fruit, peaches, and strawberries.
Also from the book, the most common method is to add fruit to secondary. Some people steep the fruit at flameout for 15 - 30 min. The disadvantage of that method is that fruit has pectins that can cause haze in the beer. If it's a hefe, you probably aren't worried about the beer being clear.
Hopefully this info helps you a little. The info in the book has definitely helped me!