This is not the most useful exploit in the world, and will be anoying. But if you're like me sitting at the 4k honor cap and sick of running heroics, this is a decent way of banking as much extra honor as you can farm in the next two days. (Season 9 is scheduled to begin on December 14th)
After you hit the honor cap, purchase any piece of PvP gear, then farm back up to around 4000. Items purchased with honor can be returned for full price within 2 logged in hours. This means if you are logged off the timer stops ticking.
You're obviously going to be logged in while you farm more honor, so be sure to keep very careful track of how much time your items have left.
After 1 hour 45 minutes or so, buy another piece of honor gear and return the first, to refresh the amount of time you can be logged in. You can fill your bags with as many pieces as you would like.
Be careful to not accidentally sell a piece that will push you over 4000 honor. To find out how much an item will return for you can right click to sell it. A dialog will pop up asking if you are sure you want to return the selected item for XXX Honor points.
I can not guarantee they won't do something about this when they patch for season 9, but I can confirm that it works for now.
Personally I'm buying Field Marshal gear. If Blizzard is clever and doesn't allow refunds of items bought pre-season 9, I'll at least have a set of banana gear to run around in.