expanding a path

[dave young]

We have a situation where we would like to pass an expanded version of a
path, defined with a <path id="xx"> tag to another task. In our case we
are using some third party executable to run a java program for some
reason (purify), so we'd like to use the <exec> task and pass the
classpath through within an <arg> construct to the command to be run.

Is this possible without writing our own custom task to invoke the
executable?

Any advice/suggestions would be appreciated.