If the problem goes away each time you regrease the BB, I suspect the source of the creaking really is the BB. I've heard of using Teflon plumber's tape in the threads, especially in non-ferrous frames, but this could be an urban legend of the equivalent of sending the new midshipman off to look all around the ship for the key to the keelson.

However another source of creaking can be the cleats of your shoes against the pedals, again especially after a rain. Try some Armour-All. Can't hurt, might work.