Any way of parametrizing whether or not to append inner elements in ant?

I am writing an ant file for compiling a flex project (but this question may apply to non-flex ant scripts as well).

I had several targets there that look like this:

<target name="first">
    <mxmlc file="${src.dir}/FirstClass.as" output="${output.dir}/First.swf" ...identical_compiler_attributes...>
         ...identical_compiler_inner_elements...
         <compiler.define name="AN_ATTRIBUTE" value="A_VALUE" />
    </mxmlc>
</target>

<target name="second">
    <mxmlc file="${src.dir}/SecondClass.as" output="${output.dir}/Second.swf" ...identical_compiler_attributes...>
         ...identical_compiler_inner_elements...

         <!-- no additional compiler.define calls needed -->
    </mxmlc>
</target>

I wanted to avoid duplication of common mxmlc attributes and inner element by using the <antcall> ant task, so I came up with something like this:

<target name="first">
     <antcall target="helper_target">
         <param name="src.file" value="FirstClass.as"/>
         <param name="output.file" value="First.swf"/>
     </antcall>
</target>

<target name="second">
     <antcall target="helper_target">
         <param name="src.file" value="SecondClass.as"/>
         <param name="output.file" value="Second.swf"/>
     </antcall>
</target>

<target name="helper_target">
    <mxmlc file="${src.dir}/${src.file}" output="${output.dir}/${output.file}" ...identical_compiler_attributes...>
         ...identical_compiler_inner_elements...

         <!-- WHAT DO I DO ABOUT THE compiler.define?? -->
    </mxmlc>
</target>

This solves most duplication nicely. But what do I do about the <compiler.define> and other inner elements that differ between the mxmlc calls? The builtin if mechanism of ant doesn't help me here - i can't invoke a target in the middle of an mxmlc element....

Any ideas? (I know ant-contrib has some kind of if mechanism. Would rather have a pure-ant solution, and not even sure if ant-contrib's if will help here).

This sounds like a candidate for an Ant presetdef task. The manual describes the task thus:

The preset definition generates a new definition based on a current definition with some attributes or elements preset.

I can't provide an example for mxmlc as I don't have Flex here. But here's an example using an exec task:

<presetdef name="exec.preset">
    <exec executable="sh" dir=".">
        <arg value="-c" />
        <arg value="echo" />
    </exec>
</presetdef>

<exec.preset>
    <arg value="hello world" />
</exec.preset>

If you run this using ant -verbose you'll see

exec.preset] Executing 'sh' with arguments:
[exec.preset] '-c'
[exec.preset] 'echo'
[exec.preset] 'hello world'
[exec.preset] 

The extra arg provided in the preset call is added to the exec.preset - which is just what you want.