Well I can think of one material that would make this easier. It's lightweight, strong, and you determine the overall rigidity. Easy to work with and wouldn't require welding.
Carbon fiber.
I tried your photo link, Are you making the hitch for the bike or is that the wrong thing? If so why is the 1/4 inch a fixed dimension? The hitch on my bike is 3/4" tubing that is welded like a truss. It bolts to the frame at the swing arm and the rear pegs. I've also seen sport bikes with a bent tube hitch that attached to the rear frame under the seat.