Carefully remove the end cap of the bat with a flat head screw driver.
Flip the end cap upside down on a flat surface.
Pour 1 oz of pourable polyurethane into the end cap and let it dry overnight.
Place a small amount of epoxy around the edge of the end cap and press it back into the end of the bat.
Let the bat sit overnight (again) with the end cap on the ground to ensure the polyurethane settles completely inside the bat.
Note: End loading is illegal in all association softball and should only be used for exhibition or practice. End loading extends the sweet spot and can increase the the exit speed of the ball.