I found this thread from a few years ago, but I'm not a welder.
So I tried hacking this together with some rubber stoppers and bungie cords.
Massive fail, it rocks way to easily. You just fall to one side and ride crooked. It's also too tall, you end up 8" off the ground without an easy way to get on and off. Oh, well... What do I expect for 30 minutes of work?