Xerces/XMLC/Java classloading question

I've started to run into some troubles trying to compile Barracuda on 
our new server box. Specifically, the issue comes down to the fact that 
we have xerces2 installed in /usr/share/java (this was a package 
dependency for Ant 1.5) which causes the XMLC compiling stuff to choke.

Now, the problem is solved in this particular instance by simply 
removing the /usr/share/java/xerces-j2-2.2.1.jar so that 
/var/tomcat4/common/endorsed/xerces-1.4.4-xmlc-2.1.jar gets used 
instead. However that doesn't solve the general problem that users may 
have a newer version of Xerces installed on their box yet XMLC requires 
a very specific (and XMLC-tweaked) version.

I'm wondering if there is a way, perhaps in the build.xml script, that 
when the XMLC stuff is done you can point it directly to the XMLC jar? 
Obviously since Ant has already started using the (newer) xerces jar 
that is in the classpath this would at least require forking a new java 
process, but I think that would be okay.

What is everyone's thought on this? Or is this even possible?

-shawn