Cushions of Concrete

Thanks to Not Martha, I have been racking my brain all week trying to figure out how I can make these fabulous garden stepping stones. I absolutely must have these and with each stone costing at least $75 after S&H, I need to make them myself. I talked to the Paleontologist at work to see if he had any ideas. (Seeing how he makes a lot of molds of old bones and all.) He gave me some suggestions so I'm hoping to stop at the Salvation Army pretty soon to pick up some pillows so I can get to experimenting. Wish me luck!