What I did was break it up, soak it overnight in water in a saucepan, added a little glycerin (didn't have to), boiled it, smoothed it out as much as I could (still a little lumpy but so are some other soaps sold), and poured it in a ceramic mug. Worked just fine.
I have a problem with dry, flaky skin in the wintertime, and to combat that, I melt little slivers of soap I collect, add glycerin fo combat dryness, and pour into cupcake molds (better if lined with the paper you can get at the store). Makes nice, soft soap to use in the shower. Soapmakers take the glycerin out of their soaps because they can make more money using it other ways.