I made a Bam biere clone, my funky blond, from the dregs, and got pretty good attenuation as I said above. The beer has really changed over time, getting lots of lemony tartness. I love it, my favorite beer I ever made.
Anyway, I just took the dregs from a bottle of Bam biere and poured them into a flask and put them on a stir plate like I do any other starter, and let it spin for a few days. I know the bugs tend not to like that, but it worked for me. I then decanted and pitched, no other yeast. My beer tastes nothing like the Bam Biere I drank from the bottle. Mine is much more sour and funky. In the brewery, the beer hits the wild yeasties in the barrel after primary, obviously in mine they are there at the front. I had a chance to go to the brew pub in Ann Arbor this past fall, and having Bam Biere on tap, it is completely different then the bottle conditioned version. Most of the difference is likely age, as the kegged beer was obviously fresh, much less funky, and much more hoppy. My bottle was probably pretty old, sitting on a shelf in a small town here in Maine, I was shocked to see it, and I think the owner was shocked I bought it.
I have since plated out the dregs from my brew, and I have isolated a yeast strain. I don't have the proper media to check to see if it is really brett, but the liquor from decanting sure smells and tastes like a strain of brett. Very...blue cheesy early on, but now getting more lemony/horsey and tart. I plan to slant some of the yeast to come back too if I have too, and I will keep the culture rolling and add it to secondaries here and there.