When I was little my gran would babysit me, and since she sewed, so did I. I used to sew "pillows" for her all the time - little hand-sewn pouches stuffed with scraps. She attached elastic to them and put them onto her machines to use as pincushions, just as you have done (though minus the index card, that's a great idea). I was so proud!
I recently inherited her old machines, and one of them still had one of my little "pillows" strapped to it. <3