Is your other horse quiet enough to pony the bucker? If so, maybe your dad could saddle up the bucker and pony him a few times before trying to get on him again. I don't know if it's a good idea for you to do this though, as I'm not sure how experienced you are.
Tiring him out the first few times before he's ridden is probably a good idea. Eventually he'll get more and more fit, though, so it probably won't work long-term. And I'm sure you're aware of this, but make sure you don't work him so hard he's injured or something.
There's definitly plenty of groundwork you can do. It's hard to suggest what to do for sure, though, without seeing why he bucked. Was he just full of beans, or was he maybe not real well-broke in the first place? Is he a cold-backed kind of horse that tends to hump up whenever he's first saddled?
I like to do basic round pen stuff with my horses, on a very long lead rope (since I don't actually have a round pen). I often even warm up my 16-year-old gelding before I get on. The first exercise on this blog is one I do a lot. But you absolutely need to make sure you are out of kicking range, especially if you've never done this with this horse before. Some horses will kick! Starting Stevie: Day Ten: Flexion
And here's some stuff from Louisiana State. You'll notice about 2 minutes in the horse is licking its lips, and the guy gives the horse a break. I like to do the same thing when they've made a bit of progress and start licking their lips, as they're thinking about what they've just done (or so I've been told).
Another thing to remember is that horses learn from releasing the pressure. So apply pressure until the horse gives you a positive response, then release the pressure immediately.
And you can certainly do this while the horse is saddled, to get him used to carrying the saddle again. https://www.youtube.com/watch?v=ieydRYGleaA