Broken down it's till 6 foot long? That's a long rod..
I did more or less what Groo mentioned , I have a "rod case" that holds several rods and is just under 5 feet. I used a short bungee cord on the bottom, lashing to the front mount area of the passenger peg/floorboard, and then used another cord around the forward sidecase mount . I wrapped the case with some foam padding where it contacted the sidecase and side panel so it would not wear a spot.
Now, I have a few rods that break down into four sections, and come with their own case. At about 28 inches long , I just bungee it across the front of the top case, or along the side of the grab rail when I have a passenger.