Modifying results XML output within test methods

Is there a way to allow a test method to modify the results XML output? For example, this is the current output of a test:

<test-case name="TestTestProject.UnitTest2.TestMethod2" executed="True" success="False" time="0.004" asserts="0">
  <failure>
    <message><![CDATA[System.ApplicationException was expected]]></message>
    <stack-trace />
  </failure>
</test-case>

Compared to what I'd like to have:

<test-case name="TestTestProject.UnitTest2.TestMethod2" executed="True" success="False" time="0.004" asserts="0">
  <failure>
    <message><![CDATA[System.ApplicationException was expected]]></message>
    <stack-trace />
  </failure>
  <text-output>
      <![CDATA[arbitrary text output goes here]]>
  </text-output>
</test-case>

Or something similar to that. The arbitrary output would contain, e.g., stdout, stderr.