My gelding also does this, and I do not tolerate it. 'Bumping' can and will result in more dangerous manners later on. Yes, you can try being gentle and nice. But with a draft? Bumping leads to biting, charging, absolute disrespect. I am very humane to my animals but there are some things that need prompt correction.
My gelding bumps, and gets a firm wack on the nose. Bumps again, same thing. I don't deck him hard, just a quick rap and a loud 'NO.'
He did this A LOT when I first moved him to my pasture. Talk about respect issues. It took him less than a week to turn those bad bumping manners into 'Okay, I get it, I won't do it'.
He does throw his head up, looks wild eyed, but only for a moment. I ALWAYS pet him gently afterwards to establish that the smack was because of the action. He is not head shy and very rarely bumps anymore, if at all.
I do not believe in stud chains, or any chain, across a horses nose except on a horse were you need absolute control. Such as on a breeding stallion, whom is about a mare in heat. Chains can be extremely severe. The only place I EVER use them is to lock my pasture gates :)
Wait! I'll fix it....