Okay, so I don't think this thread has been fully answered, if so disregard my post. My tattoo artist also brews beer so I'm basing my facts off of his experience.
Apparently THC is alcohol soluble so he took about an 8th, and soaked it in Everclear for about 2-3 days. Then he added the mixture to the secondary. Now that you have raised the alcohol content of the beer so drastically you may have shocked the yeast and killed them. So at that time you must use a yeast booster, you should be able to get them from the local homebrew store, or I know austin homebrew supply has them. Ferment for another week, rack for a second time attempting to remove all remenints of MJ. After another week your ready to bottle or keg.
I know he used a lambic, kit that he purchased from the brew supply store here in town.
I had a bottle, as a beer it turned out fantastic **you get any MJ flavor in the beer** and the high was subpar and more body high, but the beer will mess you up quick.
Once again, I'm not a professional brewer, nor did I attempt this myself. Although I am an inspiring, head brewer.