I contacted "the Mad Fermentationist", a homebrewer who has been playing alot with wild beers. His blog is here: The Mad Fermentationist
His response to the same question follows:
Brewing sour/wild beers at home is definitely a small niche in the overall small niche of homebrewers, but I think both are growing rapidly.
I started out not adding any bottling yeast four sour beers. After a year the Brettanomyces will still be active and will carbonate your beer... eventually. This is the way traditional Gueuze are made. I didn't enjoy having to wait 6 months for some of my beers to carbonate though.
These days I generally add some dried wine yeast. Wine yeast is generally more acid and alcohol tolerant than beer yeast, but I am sure that S04 would be fine in a beer like this.
Russian River and Lost Abbey both have house wine strains that they use, I just buy whatever strikes my mood at the brew shop (generally Champagne yeast). Most recently I have used 71B-1122 and EC-1118.
Another option is to add more Brett for bottle conditioning (something some breweries are starting to do), but I have yet to give this a try.
Even once it carbonates sour beers need some extra time to mellow in the bottle I have found, but less so when you add bottling yeast. I'd vote against using DME for carbonation, because it is hard to tell how much of the dextrins the wild yeast and bacteria will consume (could lead to overcarbonation).
Hope that helps, good luck getting the beer carbonated.