I'm not sure about softening the powder, but you can make your own buttermilk by adding a tablespoon of acid, either lemon juice or vinegar, to a cup of regular milk. Mix it and let it sit for 10-15 minutes.
At weddings, my Aunts would poke me in the ribs and cackle "You're next!". They stopped when I started doing the same to them at funerals. www.kyleskitchen.net