this is easy. You can construct what I call a "shelf" to buffer your forehead from your hair. All you need is a few 6 inch strips of vinyl siding, duct tape, a healthy supply of wax, and sturdy carboard. You put all that sh*t together and you end up with this really ugly and uncomfortable helmet thing. Tape the shelf to your forehead and you should be able to keep out the shampoo.
***WARNING: The "shelf" doesn't work at all, under any circumstances. Not only do you get more shampoo in your face than you would without the shelf, you also get bloodied lacerations across your brow. I have a large dent in my forehead now in the shape of the letter "V" as a result of using the shelf********
good luck with the shelf, hope it is helpful,
Dick Van Dyke