Simple answer is you can't get rid of it this late, but you can try to control it.
Under no circumstances should you apply a product that could harm you or anyone else by consuming the ganj. Nerve damage is no joke, and can last a life time.
Try wiping leaves off with clean rag and maybe a tiny, tiny, tiny, bit of dish soap. (Like 1/2 drop soap into a gallon of water, then put that solution on a paper-towel or soft rag.) In future runs ensure adequate airflow circulation and make sure temperature of your room is kept in check. (meaning not widely changing between lights on temps and lights off temps.)
I don't think this will completely solve your problem, so my second suggestion would be to thoroughly pluck fan leaves from your plants before hanging to dry, so that any of the fan leaves covered with Powder Mildew will not spread to the drying crop.
I may be mistaken about this, but i think Powder Mildew could also be systemic, meaning the mother plant could've been infected and the clones inherited it. Make sure your source of clones is clean too.
