As others said, tie the loose horse up. It takes a good horse to not want to buck or run off when a loose horse goes tearing by.
Another quick word of advice, don't pull back on both reins when that happens, pull the nose one way or the other. Keep forward movement you can control, a very small circle.
Don't be scared of him, you know what caused him to buck. If you know the cause and you know how to prevent it you have the power to stop it. Also, yes, you can lunge in the snow. But don't do endless circles trying to wear him down. Switch directions often and as soon as he is paying attention get on, trying to wear one down before riding only makes the horse stronger and it will take more and more time before you get on and even at that he still may not be paying attention.
I DON'T LEAD 'EM AND FEED 'EM, I RIDE 'EM AND SLIDE 'EM.