I'm a believer in adding commercial dregs/repitchi
I brewed a Flanders Red in June 2008 w/ Roselare in the secondary. It never really got sour and only fermented down to 1.011.
I brewed a second batch in May 2009. I pitched a fresh pack of Roselare into the primary, and added a pack of Coopers after 48 hours. I also added some slurry of WL brett C to the secondary. It never got too sour either, and only fermented down to 1.011.
I blended these 2 batches and won silver in the 2010 2nd round NHC as an Oud Bruin. It is a nice Oud Bruin, but not what I want. I only bottled half of the blend, and kept the other half.
So anyways, I brewed a 3rd Flanders Red in Jan 2010. For primary fermentation, I repitched the Roselare slurry from the secondary of the second batch and added Coopers after 48 hours. I mashed this one really high (156F), so it went into the secondary at 1.020 (the first 2 batches went into secondary at 1.014 and 1.016). Over the last 6 months, I have added dregs from Lindemans Cuvee Rene, Petrus Aged Pale Ale, Cantillon Lou Pepe Kriek and Mikeller US Alive!
I decided to pull gravity samples yesterday. The blend of 25 and 14 month old Flanders is still sitting at 1.011 and still tastes more like an Oud Bruin. However, the new 6 month batch is unreal! It's down to 1.009. Very funky, with lots of tart and sour going on. I couldn't believe how good it was tasting for such a young sour - it was very complex and didn't seem harsh/undeveloped.
I suppose it could be a combination of 3 factors - repitching roselare, mashing high, and adding multiple commercial dregs. But whatever I did, it sure seems to be working. I can't wait to repitch this slurry into the next batch which will be brewed in November.