OK, so in case anyone else ends up having the same challenge I did, here's how I solved it. I wrote a new plugin, and included the following code:
function hidefromrss( $content )
{
// in case we want to add to earlier versions
if ( is_feed() )
{
$dom = new DOMDocument;
$dom->loadHTML(mb_convert_encoding($content, 'HTML-ENTITIES', 'UTF-8'));
$xpath = new DOMXPath( $dom );
$pDivs = $xpath->query(".//div[@class='hidefromrss']");
foreach ( $pDivs as $div ) {
$div->parentNode->removeChild( $div );
}
$content = preg_replace( "/.*<body>(.*)<\/body>.*/s", "$1", $dom->saveHTML() );
}
return $content;
}
add_filter("the_content","hidefromrss");