If the ball and spring are gone, the first step is to open up the peened part of the hole. Find (or make by grinding) a tapered punch that will fit inside the peened part of the hole and that will enlarge it to the unpeened diameter by driving it into the hole.
Once the peening is removed, figure out that diameter bearing ball you need and purchase one. Then find a spring that will fit the hole diameter and which is the right length to hold pressure against the ball at full extension, but will also collapse enough to let the ball retract flush with the surface of the square face.
Now the hard part. You need to peen the edges of the hole while the spring and ball are installed, and the ball isn't bottomed against the fully collapsed spring by the peening tool. If the hole is deep enough, a flat-faced punch may work. If the hole is too shallow for this, then the peening tool needs to have the center relieved enough to let the ball sit out a little. I've never seen the factory peening tool, but perhaps someone will be able to describe one.
Good luck! I think it is do-able.