I've suffered with a coated tongue for years and it only gets worse with VLCDs. I always use a tongue scraper every time I brush my teeth. The other thing I found really helps is eating probiotic yogurt. So I put a desertspoonful of fat free Rachel's yogurt into the fruit flavour shakes. - It is disgusting with vanilla or chocolate though. If you aren't following Total Solution, it might help to try that. The calories are negligible.
I also keep a glass of water on my bedside table, because I wake in the night with a tongue like dried out cardboard on this diet.