Adding the fruit to the beer will dilute the sulfites below the inhibition level for yeast (brett and your sacch strain).
I know breweries use sulfites to kill wild yeast on fruit/veggies before adding to clean beer (Flat Tail in Corvallis comes to mind).
As far as prep for the fruit:
The fruit will add fermentable sugar for consumption by either your primary sacch strain or brett. If you want brett to ferment these sugars, make sure you leave as much sacch behind as possible. Fine and cold crash in a keg if possible, then pitch a healthy slurry of brett. No kegs; no worries, just fine in primary before transfer.
If you want to turn this around fairly quickly (or if you started with a fairly hoppy saison), I would chop the fruit or puree with a bit of lemon juice and water.
If time is not an issue, or if you might add lactic acid bacteria for acidity, just chuck 'em in whole and rack on top.
Let us know how it turns out!