You can do big rosettes - i've seen them done before on arabs since they have healthy, full manes...it is against their show rules to cut the mane so they do hunter rosettes but larger. I know it isn't original, but in endurance, we just do lots of regular braids and let them hang down. As long as they are uniform in thickness, evenly spaced and looks tidy, they will still be pretty even as plain as it might seem. Good for you for keeping the mane long!
But for jumping, try the rosettes - it might not be as hard as you think once you figure it out - kind of like tying your shoes - soon you can do it with your eyes closed. But for the rest of your events, especially reining, put some showsheen in it and a little pomade (to keep it from being frizzy) and let it fly!
Here are large rosettes you could do for jumping - never know until you try large rosettes.jpg
And this one I just ran across by accident and decided to throw it in here just for the WoW factor!!!!!! plaits.jpg