I'm no lady but this might work. Draw or find a simple shape (or shapes) you like that fits in the snowball. If the quilt is winter themed maybe something like simple snowflakes or snowmen would work. If not then maybe simple flowers etc. Make as many copies as you have snowballs and pin them to your quilt. Then just sew over the paper following the lines and tear the paper away when you're done. A clear space like a snowball is just begging for some decorative quilting in it.
Rodney