Once you collect enough soap slivers, you can make them into new soap bars. You can add colours, fragrances, and other ingredients, and make it into any shape you want. Generally you'll want to grate or cut the soap, melt it, then mold it. There are a handful of ways to do this, here are some good guides:

• tutorial on Howcast – boil, then mold
• make Soap Balls – grate, then form by hand
• tutorial on Instructables – cut, then microwave

You can also grate them (or add some water and use a blender) and add it into your liquid soap bottles.