In my code I use the convention of m_varName for member variables. I would like a policy that removes the m_ from the variable name. Very simple really. And I'm also only concerned with java to json, but it would be pretty easy to match varName to m_varName.
I understand the desire to not complicate the API, but restricting functionality only hinders adoption of your code. Besides any complicated API can be simplified via good documentation, which you have done pretty well at.
Brian