Twleve inches is to much remove. If you had asked about 1 or 2 inches my answer would have been different.
To recommend a solution to what you want to do I ask this question, is it possible to slip the antenna into a small flexible plastic tube and snake it back and forth inside the fuselage ? You will want the curves to have the biggest radius possible. Since 12" would have been sticking out I must assume that it is a small plane, being a small plane means it will be flown fairly close in, or at least with my eyesight that is what it would mean. Having the antenna less than fully extended will reduce the range somewhat, but we have a lot of range to spare, if the plane is small and flown fairly close in you should be good to go.
Unless an electrical engineer has published the instructions I do not recommend wrapping the wire around anything to create a coil. While it is possible to make a coil that will enhance the performance of the antenna it needs to be an engineered solution and it needs to be measured with test equipment to verify the design.