I am pretty positive I am not the first person to think of this, but I like the idea! I also figured out a pretty simple way to do it. All you need is a mason jar used for canning (meaning the lid has 2 separate pieces: top and ring), a hot glue gun, a scrap of beautiful fabric, a little pillow stuffing, and some scissors.
I cut my scrap of fabric with a radius approximately one inch larger than the top of the jar. The fabric needs to be bigger than the top of the jar because it is going to end up being 3D rather than flat once it is filled with stuffing.
I will warn you in advance, I don't have a helper, thus I could not take pictures of myself gluing or actually performing some of the steps. If you are trying to do this and anything is unclear, do not hesitate to ask questions!
Ok so, I found the easiest way to go about this was to place the fabric on top of ring (right side toward the ring) and then the stuffing on top of the fabric. We are not gluing anything yet because you want to make sure you have enough stuffing to make your pin cushion appropriately dense.
On to gluing. After you are comfortable with the amount of stuffing you have added, you want to tack the fabric down to the 'top' part of the jar lid. It is best to do this while it is inside the ring to retain your shape. Just dab hot glue underneath the edges of all of the fabric that is sticking up. The end result should look something like this.
Now, we still have not glued what I refer to as 'the poof' into the ring itself so you should not have any trouble popping it out like so.
You can then quickly run a line of hot glue around the inside of the ring. You will see that there is a lip that your poof (or normally the top of the lid) would sit on. This is where you want to put your hot glue. Then you quickly shove the poof back into the ring, and press it firmly against the lip of the ring until the glue sets. When you flip it over, it should look like this!
Once that is done, the jar is free to be used as decorative storage! These are great for thread, scraps, buttons, beads, zippers, you name it. You don't even have to use the 'poofs' as pin cushions. They can be labels or identifiers so that you can keep your jars organized. Personally, I can never have enough places to stick pins. I find myself desperately searching for anywhere to put them while I am mid project. Haha. Hopefully you'll be able to create some great storage solutions with this fast and easy project!