Sorry, I've been away for a time. I doubt this is still something you need, but what the hey.

I use s system where H2 tags mean a test name and H3 tags mean an expected value and a dynamic value sooo

<h1>My Tests</h1>
<p>Heres some text that my parser will ignore!</p>

<h2>SSI ENABLED</h2>
<h3>foobarbaz</h3>
<h3><!--#echo "foobarbaz" --></h3>

<h2>SSI EXEC PROHIBITED</h2>
<h3>[error: exec forbidden]</h3>
<h3><!-- #exec cmd="echo Holy Crap" --></h3>
[download]

Writing the parser as a nagios module is an exercise left up to the reader...

Also, the SSI above is made-up and won't really work.