I haven't done it, but it seems like you could cut a long handled spoon in half, punch a hole in each section, overlap the holes, and toss a small bolt and wingnut through the hole. When you want it long, just rotate the handle out and tighten the wingnut so it doesn't spin on you while eating. There may be lighter methods than a bolt and wingnut. Other than adding weight, this would make the spoon a bit shorter because it would have to overlap.
Another option would be to chop the spoon in half, then take each end and form it to a circle. Make the one end bigger than the other and then you can wedge them together.