Use either padded fabric, or any other leftover fabric. (A little bit of fiber fill if you are not using padded fabric)
a small piece of thread.
Even super tiny scraps work. Cut off excess and un-tie.
Make a rectangle that is as twice as tall as you want your pencil grip by 3/4 of and inch.
If you are using an unpadded fabric, stuff lightly with fiberfill.
Fold the ends of the fabric in and match.
Sew along the short side and trim excess thread.