My sister's method for making cookie cutter soaps saves you from having to remelt the soap scraps. Here are her instructions from an old newsletter:
This is a great option if want to make a few seasonal soaps to decorate your bathroom or include in gift baskets. You will need some waxed paper, cookie cutters and your melt and pour soap. The idea is to melt a small amount of soap initially, slowly pour a small puddle of melted soap on to the waxed paper that is just a little bigger than your mold and set the mold into it and allow it to set until firm. Then you just have to melt enough soap to fill the cookie cutters up, spritz the soap that is in the bottom of the cookie cutter with a little rubbing alcohol to make the layers adhere and pour in your soap. Since initially I was just melting enough soap to make a few puddles on the waxed paper, I used a small container and microwaved the soap in 10 second increments. Small amounts melt very quickly and you never want to over heat melt & pour soap. Once your soap has set just push it out. The excess soap will break away.