Read through the GP arf float manual... shows how they did the float mounted servo set up.
http://www.greatplanes.com/manuals/gpmq1882-manual.pdf
I went with cable myself... I may regret this later but for now I'm happy with the way it works and ease of removal/install. you'll probably need to do something for lateral balance as well if you move the servo into the float... 2 oz moved that far out is bound to make a difference.
John