Have you tried a pelham? That works much better for my freight train horse than an elevator does. My guy hunts in a corkscrew pelham (yeah, yeah) with a really tight curb because he just absolutely takes off—because he loves it that much. I’ve tried milder bits, but by the end of the day, my arms are like rubber and slowing him down turns into a huge battle that I end up losing.
I would think if you change the bit to something he respects, then that might stop the bucking issue. As soon as he starts to put his head down, you would be able to get him back up and paying attention.
Edited to add: My foxhunter was aced before going out. I was a junior, and he was an OTTB, so it was deemed the safest thing to do. It worked well. By the time the ace wore off, he was tired out and used to things. He never got much, maybe 1/2 cc, just to take the edge off. Sort of a nice cocktail, or shot of Irish courage.