simple, take a piece of 1 inch aluminum plate, drill a hole the same size as the tubing in your guard. next mark out a nice shape around the hole that would allow two bolts to go thru, one on each side of the hole, cut it out with a bandsaw, then cut directly across the hole so your bolts when drilled will clamp the two pieces together.
sorry for the crappy description but I'm getting pressed for time.