Can I build an Apache Ant task and execute it in the same step?

Question

Is it possible to create an Apache Ant build.xml that can create a task in one target and subsequently use it in another target?

Here is a simple build.xml to illustrate this:

<project name="BuildAndUseTask" default="use-task">
    <!-- Define the task -->
    <taskdef name="testtask"
        classname="org.example.TestTask"/>

    <!-- Compile the task -->
    <target name="compile-task">
        <javac srcdir="task/src" destdir="."/>
    </target>

    <!-- Use the task -->
    <target name="use-task" depends="compile-task">
        <testtask option="something"/>
    </target>
</project>

The output I get is:

Buildfile: /path/to/build.xml

BUILD FAILED
/path/to/build.xml:5: taskdef class org.example.TestTask cannot be found
 using the classloader AntClassLoader[]

Is this possible to do this as a single step without resorting to using nested Ant executions? I am working around this separately by first commenting the <taskdef>, explicitly building the compile-task target, uncommenting the <taskdef>, and finally build the use-task target.