Alright, several interesting ideas here. First, we need to define what is and isn't a "high" brace. For example, what wcf3 describes (and which is great technique which I fully agree with), I really wouldn't call a brace stroke but more of a hanging draw stroke or a gliding draw stroke since the paddle is near vertical and the support comes from being able to pull the blade towards the boat or push it away from the boat.
There a couple of possible definitions of a high brace. The first is simply when the power face of the paddle is facing down and is what contacts the water for support (i.e., wrist cocked back), regardless of arm position. This is the classic definition of a high brace and is perfectly acceptable if done properly (more on that below). In fact, almost everyone uses this bracing technique. Conversely, the classic definition of a low brace is when the non-power face of the blade is use for support (wrist cocked forward). The second possible definition of a high brace is more like what Nealy shows in his cartoons - arm and hand opposite the supporting blade raised high above the head and hand and elbow on the supporting side up and well away from the body. If this second definition is what you mean by a high brace, it is always a No-No.
If by high brace, you mean power face down, here are some tips:
1. Keep your elbow as low and as close to your body as possible. Your elbow on the side opposite the brace should be glued to the side of your body near the bottom of the rib cage. Your elbow on the bracing side will of course be away from your body, but keep it low, it should always be below your shoulder.
2. Glue the hand on the opposite of the brace to your nipple. This will keep it in front of your body and in the box.
3. Keep the hand on the brace side as low as possible and always in front of the shoulder. Use torso rotation if necessary to keep the hand fromgetting behind the shoulder.
4. If you are doing a snap brace to prevent a flip, throw your head and torso to the side of the brace (ala EJ's video)
5. Practie A Lot. It really takes a lot of practice to remember to keep the elbows and hands in and down. So do it every time you are in a boat. Also, ask for feedback from your fellow paddlers. A lot paddlers don't even realize how high there elbows and hands are so ask someone to watch you and let you know.
"It's All Good"