I'll second perhaps tweaking his diet. My horses go on roughage alone unless they need the grain to keep weight and condition - they just don't work hard enough to need it. Scout gets free choice good grass hay and turnout, plus literally a tiny little handful of Blue Seal Strider formula as a "supplement." The type of hay that you're feeding can dramatically affect energy levels as well - usually alfalfa hay makes them hotter than grass/pasture hay. I'd do a little research on what you're feeding him, and figure out if there are lower-energy alternatives out there.
That being said, your issues at shows are not just because of the show - the more stressful, high energy environment brings most horses' training gaps and holes right to the surface. You said that he has a hard time standing still "ever?" If he can't stand still at home, it won't happen at a show. Start very small, in hand, and work up to mounted later. Just ask Specs to stand. When he does, wait for three Mississippi seconds (or however long he can hold it without fidgeting), then walk him out of it and praise him. Don't praise with food at this point - he'll just start trying to nose through your pockets, and you want him to focus on you and your directions, not food. Work up the time. When he can stand for 3 seconds easily, ask him to try it for four. In less time than you think, he'll be standing like a soldier for however long you want.
If he does start fidgeting, don't fight him. Ask him to move his feet in a way that you can direct. Put him up onto a trot, forward and working, with lots of transitions and changes in direction. Get him thinking. The more you can move his feet, the more you can influence his mind. When you feel him soften and relax in motion, ask him to halt and stand for three seconds. If he stands, praise and walk him out of it. If he fidgets, rinse and repeat. This way, he learns that standing is an easy way to not be put to work, and that fidgeting earns a harder job.
The difficulty will be that this kind of technique, while it does work in many many cases, is that it does take a good bit of timing and feel to work its best. Timing and feel are skills that oftentimes only come with many years of practice and experience. Because of that, I do recommend at least consulting with someone more experienced in training horses in person. It doesn't have to be a pro trainer. It can be an experienced horsey friend or neighbor. Also, a lot of riding instructors or lesson barns will allow students to "pay" for their lessons by cleaning stalls, grooming horses, etc. Then, your only constraints would be time and a ride to the barn.