Im so curious on what your solutions is, that I just made an account here.
Here is a comparison of the raw GH2 footage vs. graded footage. (Too red but it's a grade:P)
Personally I think this is really FLAT enough to use for grading as such.
Why would you want even more FLAT than this with a risk of losing your range since it won't get any better than 8-bit 4.2.0...
Hope you can surprise me!
http://vimeo.com/41629648