Appending to system classpath in Ant

[Brent Kyle]

        I'm a big fan of Ant, but I'm currently stuck on a problem.  

        Normally my Ant build files just use the system Classpath.  However,
now I need to append about directory to it, but only for this one Ant build
file.  I can't find anything in the docs on how to do this.

        How can I access the system Classpath variable so I can use it to
append a directory to it?

        Thanks for the help!

-Brent.