To attach a bobby pin to the back of a silk flower, cut a rectangle of fabric that's about 1/2-inch wide and about two-thirds the length of the bobby pin. Slip the fabric into the bobby pin, and slide it all the way to the other end of the pin. Lay the pin facedown on the work surface (so the flat side of the bobby pin is facing up), and apply fabric glue to the small piece of fabric.
Then attach the piece of fabric, with the bobby pin still in place, to the back of the flower. Let the glue dry. The fabric will hold the bobby pin in place.