You could always use a URLClassLoader to load classes from jar files that aren't in the classpath. You'd have to know where the jar file actually is, of course, but presumably the user is going to tell you that somehow.
I've given urlclassloader a "run out" and it doesnt do quite what Im after...
I was hoping for something where I could specify just a directory and it would load all the jar files within it amd as far as I can see you have to specify the jar file by name or a base directory where the ".class" file can be found (within a package directory structure).
I've a feeling I'll have to create a custom classloader !