Any ideas for correcting Flathead Syndrome?

My daughter is 6 months old and she has developed flathead syndrome. The whole backside of her head has flattened because she spends a lot of time laying on her back. She doesn't really like Tummy Time although I keep trying and she's gettign a bit stronger. I tried to tilt her mattress so that she would turn her head and that kind of backfired.. she ended up rolling into the corner of the crib and screaming. I've been researching this condition and really the only answer seems to be to get one of those moulding helmets for her. Are there any other suggestions??? I've read that if you don't treat it befor 6 months a helmet is likely the only option. Has anyone had a child with this issue that was able to correct it after 6 months of age??? Any ideas would be greatly appreciated!