Chances are you don't have any wild cultures in there other than Lacto. And, if you do, they'll be "overpowered" by the dregs. Brett is not easily captured in my experience but Sacc and Lacto seem to be everywhere. Also, I highly doubt you've got a pellicle forming. They take a while to form and don't like movement a lot. IMO, if you want to pitch it next weekend, step it up and pitch as you would any starter. Looks like you've already got a quart starter there so it shouldn't take a lot more to take off well in 5 gallons. Just don't expect anything other than the yeast Saison du Buff is fermented with.