This was a very early morning thought i had and i put it on paper to see how it would look, hardware store, bolt where tripod screw mounts, some of those galvanized flat stock as many as you need to make it secure, next 2 pieces of the angles, bolt them to the end hole of the flat stock pointing down, next two more pieces of flat stock as long as you think you might need and sharpen a nice point on each one them, you can mount them to each of the angle brackets and bolt them together, drill more holes in the flat stock or you could make a long slot also, this way you could almost have any angle you want to shoot at, up or down.
Since the ground is hard yet hammer the pointed ones into the ground first then mount the rest of it together.
Going to try mine out this weekend, like i said it was an early morning thought, took only like two minutes to put it together, or maybe any engineers out there could explain it better than i did.

Mike.