Just be honest and polite, worst case scenario, swap it for an addy of your choice and use the PTB on your next floor. I tend to find that most people appreciate the fact that you've researched your fixing materials etc. if BAL say no, surely he won't want to have his bathroom tiled with a product that might fail. I'm sure it won't fail, your problem will be getting it onto the wall! If you read the PDF, it says that after you have poured it, it needs to sit for 3 mins before troweling, if that's on a wall, I think most of it will be on the floor after 3 mins. Don't worry too much mate, wait and see what BAL say.