I did this last year and had to open the sides of each holder a wee bit. Just at the back “behind” the bolt/stud. I then slobbered up the pad with rubbing alcohol and nose dived it in and over the stud. Bent the sides back into place. That may be a death sentence for the holders but they will work for the rest of my sorry ole life.

Note: once installed on the bike, I found the pads were too thick. They left no room for adjustment and insufficient brake cable tension. The holder itself is thicker than most (ex: Campy) pad holders due to that hump in the center where the “bolt” is. I removed them and carefully milled 1 to 2mm of red rubber off each pad on a disk sander. Long time to set up that procedure, seconds to do the sanding. Now they’re fine.