With a combination of Gary's suggestions and those from a post from another board here
http://www.sunlineclub.com/forums/f71/dicor-questions-17713.html (dangit, still can't figure out how to embed a URL) I finished the project and can report, yes non-self-leveling Dicor can be tooled. Within limits.
Masking tape helped tremendously, creating defined bead edges and transforming the result from my typical "Rank Amateur" status to "Owner-modified but not too noticeable."
The soapy-finger tooling method works well too. I don't know if the liquid worked more as a lubricant or simply retarded the creation of the Dicor "skim," but it worked far better than a bare finger.
I found that time was not my friend. Applying the masking tape is not so time-sensitive but from the point that the Dicor comes out of the tube until a skim begins to form, there's a limited window, not more than a couple of minutes, to perform whatever tooling will be done. After applying the material is not the time to visit the bathroom, partake of beverage, check on ball game scores, etc. A four-foot bead was about as long as I wanted to apply before beginning the tooling process. The masking tape needs to come off sooner rather than later, too.
I placed all of the masking tape then began applying Dicor on less-visible surfaces, those you'd have to bend over and crane your neck to see. That gave me some experience and kept learning-curve boo-boos hidden from cursory view. It also got the unpleasant arms-overhead part of the project out of the way early.
It's a messy job, requiring lots of rags/paper towels, and soap and water. Sprays of Coleman gas on my hands worked more quickly than soap-and-water.
