I don't know if I'd mentioned it before, but I was having a hard time seeing behind me on the Sportster. I had a really good view of my shoulder or an OK view of the next lane, but seeing behind me was almost impossible.
It's kinda hipster for this old guy, but I decided to relocate the mirrors under the bars. Fortunately, my waist isn't quite as wide as my shoulders (I have a friend or two who can't say that), so putting the mirrors under the bars made it a lot easier to see around and behind me.
Krator makes a mirror relocation kit I noticed on Amazon so I ordered it to give it a try.
It's basically a short arm that attaches to the underside of where the stock mirror is set up. You can use your stock mirror (which is what I did) or use any other mirror you want.
In addition to the lock nut you're already using on the mirrors, it comes with all the other hardware you'll need. There are no instructions, but once you start working with it, it's pretty obvious what you need to do. You'll want to attach it to the underside of your lever housing to give you enough clearance underneath the bars. They also give you a handsome castle nut to use on the top so it doesn't look like a totally kludgy installation.
You will need to make sure you have the mirrors adjusted so they they don't hit your tank at the stops—or you will have a few nice words to say. The left and right mirror set up is not exactly symmetrical, so you can't just assume what works on the one side will also work on the other. Be prepared to play with it just a little bit, but it does work and is pretty easy. I guess it could be problematic if you have super low slung bars, but I think you should still be able to make it work.
I like these better than the bar end mirrors because it doesn't add anything to my width profile, but bar end mirrors would give you the same kind of view behind.
After an hour buzzing around town to give them a good test, I like that I can see behind me and feel good about the purchase. It's not something I would have thought of had I not seen it done on a cafe racer or two, but it does work and I don't mind being confused with a much younger guy when I'm on this bike—if you know what I mean.
UPDATE: After riding with this set up for nearly a month, I'm glad I did this. No regrets. I have a great view of what's going on behind me. I would totally do this again.