Common misconception, Brett. is not sour. It is bacteria that makes the beer sour, i.e. Lacto and Pedio. Brett. does however do well in a sour environment (pH=4.5). Brett. is more barnyard and funk.
If you are doughing in at 104F, my guess is you are doing a step mash? My concern with doing a cereal mash and then adding it later would be that you are running it through all of those enzymatic steps a second time and would break down all of your sugars and starches in your wild rice further, possibly leaving your beer thin and insipid? I know saisons are supposed to be crisp, dry, and effervescent, but that may be a risk of "re-mashing" your rice after you have gelatinized all of the starches. But, it is all assumption, I have no practical or scientific info to back it up.
Here are a couple of good links on cereal mashing:http://www.winning-homebrew.com/cereal-mash.htmlhttp://www.ingermann.com/cerealmash.htmlhttp://486286.cache1.evolutionhosting.c ... ilsner.pdf