If you have never made a mold before, and want to avoid the hassle, let me offer a suggestion: While I was in the local toy store looking at the plush creatures, I came across the ones made of stretchy nylon and filled with plastic beads. I don't know their propper name, but they are soft, supple and stretchy. I saw the snake figure and thought that it would make an excellent headtail.
So I suggesting that the lekku be sewn lycra and filled with polymer beads. They would be flexible, light, and move nicely.
My $0.02