I briefly referred to using a downspout for a soap mold in an earlier post. Here's how that works.
Go to your local lumber or building supply store and purchase a section of downspout for gutters. Downspouts come in a variety of patterns - some plain, some ribbed in various ways. Get the plastic one. They are usually about 8 feet long. Get 8 end caps that fit the downspout while you're there. While this could be the most costly tools in your soap making collection, these can be used for many years so the cost really works out nicely.
When you get it home, cut it into one foot sections with a hack saw. It's pretty easy to cut. Place an end cap on each one, but don't glue it into place. You'll want to be able to remove it later.
When you make your soap, pour the traced mixture into a capped downspout. If you make a lot of soap, you'll want more sections, but one will do for a small 3 pound batch of soap. After the soap cools thoroughly, remove the end cap and push the soap out of the mold. You'll have a soap "log" that you can cut into bars. The thickness is up to you, but I found that about 1 1/2 inches worked out nicely for generous sized bars of soap.
The soaps will be very prettily shaped when you use this method.
