Maybe you can pour a small amount of plastic (on whatever surface). Then, with a rotary type tube tail cutter, cut thin strips. Adhere the strip to the middle of the insert, then shoot. Or, possibly, melting the ends of the strip together to create a rubber band and slipping that over the insert? If it was a tight enough fit, it might just stay in place. You might have to put a notch in either end of the insert to hold it in place.