This beer is useless without weed.
Nah, just bustin' yer bong. I doubt you'd notice the difference between the JBM and any other decent coffee in a porter. I'm not saying you shouldn't do it, but I'd drink the good stuff and get something else freshly roasted for the beer.
Converting from 1 to my usual 5 gallons seems to indicate the recipe is fine otherwise, but I've had a few already, so await other replies to be safe.