Step 1: Turn the garment inside out and place a scrap piece of material behind the existing hip pocket.
I used a scrap from an old surplus military jacket that I am using for another project.
Step 2: Trace the outline of the pocket onto the scrap material.
Step 3: Sew the new pocket to over the existing hip pocket.
I folded the leading edge of the new pocket before attaching it to prevent it from fraying. Be careful not to sew too much into the existing pocket and check to make sure that you did not leave any holes where something could fall out. Once the garment is turned right side out, the pocket will hang un noticed from the original pocket. The only downside is you will have to think of creative ways to stick your hands down your pants to retrieve whatever you have hidden there!