I keep threatening to do this and there are several articles out there on doing it. I've hesitated to commit 15 lbs of grain to the experiment because my commercial brewing friend tells me that some craft brewers that bottle condition use a different yeast in bottling than they do in producing the beer.
If you remember my first post here, it was about getting yeast to stick to the bottom of the bottle. My masterbrewer friend told me that when he bottle conditioned, he used lager yeast, even in ales, because it is more sticky when it falls out. I've had some improved sedimentary stability (totally made-up phrase) from pitching a bit of champagne yeast with the bottle charge.