My understanding is that it is somewhat of an inexact science/art to blend sours and especially to bottle condition them. For the latter, you would need to have a pretty extensive understanding of not only the specific gravity, but the composition of the residual carbs in the finished/blended beer. That being the case, we are likely bottling 15 gallons or so of year-old flanders shortly, not including any blended young beer.
Is the simplest way to ensure a consistent carbonation level to pasteurize the beer then add new sacc yeast with priming sugar? Or would a potassium metabisulfate+potassium carbonate combo work on dropping out all the bugs like it does with yeast in ciders/wine?