Ant Tasks defined in typedef

Trying to include the M2 Ant tasks with typedef doesn't work. The script snippet to do that would be:

<path id="maven.classpath">
<pathelement location="${setup.lib.path}/maven-artifact-ant-2.0-alpha-2-dep.jar"/>
</path>

<typedef resource="org/apache/maven/artifact/ant/antlib.xml" uri="http://maven.apache.org/maven2">
<classpath refid="maven.classpath"/>
</typedef>

Running Ant with that snippet gives the following error:
C:\Chris_Web\nfpnet\build.xml:75: java.lang.IllegalStateException: The internal default plexus-bootstrap.xml is missing. This is highly irregular, your plexus JAR is most likely corrupt.

The reason why I need the typedef is because I need to specify the location of the JAR in the build file because I dynamically reload/fetch it from the web from another Ant script.