I don't know direct, elegant solution working with jars but some time ago I did this:
when you say in your app "import com.something.AClass;" compiler searches for that kind of directory structure. I just extracted jar I was using and made sure it has proper directory structure. In this case that would be "./com/something/AClass.class". It worked.
While this works I'm pretty sure there is a better way to do this, like just including jar or something. Other experienced ppl will hopefull tell us both