Probably the final installment in the "harp ornamentation" series...
I presented my musings to my teacher, Cynthia Cathcart, last night. Her take? "Arrange the ornamentation." I explained that I was looking for ways to improvise ornamentation, and she suggested her "bag of tricks" approach. Which is, essentially, learning lots and lots of ornaments and then sticking them in where they fit a given tune. We didn't get into details, but my feeling is that anything one calls a "bag of tricks" is learned mostly through application.
That is, while Cynthia did say that one can practice ornaments in isolation, it's more... natural? to learn them as preplanned parts of other pieces. Ornamental repertoire grows along with melody repertoire, and you have real experience in how they fit into a melody. That certainly makes a lot of sense.