While you can't use V4's rig for the Dryad, you might be able to use a rig from an open source figure such as the Project Human figures.  I qualify this as a might because I'm not 100% certain of this.  You might try the copyright forum.  They are likely to have a better idea about this.  You could also contact Sixus1.  They are the original creators of the Project Human series.  Just a possibility you might consider.