If you actually want to add lactic acid for a slightly sour flavor, do it after fermentation or use an acid producing bacteria.
Or, you could add some sort of acidic must or fruit. I made a killer Saison last year with a bit of grapefruit juice.
Yeah, after tasting this one I've decided that I'd much rather use a basic saison as my base for fruit beers instead of something like a Blonde or American Wheat. 3711 will be in heavy rotation in my brewery this summer. I definitely want to brew a Hibiscus Saison as well as something using juice from a white wine kit and Nelson Sauvin hops.