If you think it's becoming a problem then I would just stop the morning bottle altogether. If you stick to just offering milk in a sippy, straw or open cup he will get the message that there are no more bottles in the morning. I am sure he will protest for a few days but he will come around to it. You can stick with offering a cup of milk with breakfast and again with a mid morning snack. Don't forget they don't need milk to get their dairy and at this age they only need around 12-14oz, so you can increase the dairy in his food if he decides not to drink as much.
If you decide to go cold turkey make sure you stick to it though, if you give it back it will be harder the next time! He will still have his bedtime bottle so he wil get a good drink of milk at bedtime.
Laura