Everything I've read has said to add the fruit after the initial ferment. So you would ferment it then rack into your secondary with the fruit in there. The ferment will take off again, but not as vigorous. But if you do this, you will want to allow enough time for the mead to clear before bottling.
And technically, you will no longer be making mead. Depending on the fruit, you could be making a melomel, cyser or pyment. There's also other types that have barious spices in them.
Good luck with your mead and please report back how it turns out.
