You should instead consider the second stem option if you have a threadless type stem and enough steerer to install a second one. Then a short piece of hacksawed off handlebar from the used bin at the bike shop or perhaps a piece of PVC pipe. I have not used a second stem, so I have no photos to show what I am talking about. Perhaps someone else will provide a photo?

If you have a quill stem, I have no suggestion other than look around for a 1980s style handlebar bag that hung from a steel rod frame. They are occasionally available used. I had to make a new steel rod frame for mine, the threadless stem and the old frame that was designed for a quill stem did not work well together.