Just fought with it for about two hours. Finally came up with a pretty slick solution. I went to the local hardware store and picked up some push on clamps/washers. The kind you push onto a bolt or rivet and tension holds it in place. I picked up six (all different sizes) for less than $2.00. After some trial and error I found the right one. I would recommend a couple of things:
1. Put a larger washer on first to make sure the push nut has something to push against.
2. Use needle nose plyers to lock the post in place when starting and pushing on the push nut.
2a. this was much easier after I "accidentally" broke off the mounting bracket of the torx screw with my plyers
3. Adjust the light to almost the proper height using the directions provided in this thread before pushing the push nut all the way on.
4. Finish it off by twisting the adjusting bolt to provide extra tension.
Here is a picture of the push nut I ended up using
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