I've thought about this a few times. Using hose clamps or u bolts would be the easiest. But I work in machine shop and have accumulated a small stock pile of aluminum. If I could find time to get on a mill, I could make some brackets.
i have used the us choppers mount on customer's bikes and it is a real nice part. personally in the past i have used fender stays in a jiff, on the hooligan i used skip link chain that i tack welded to the frame. i have also used small plumbing clamps they come in 1/2 inch which works great for most old frames.