Hello
I think there is no solution because i have the same probleme
In fact the design of opened articles with "read more" button is linked with the design of the category of articles.
for the plugin "p2_news", in news.php you have this code :
Code:
echo '<div class="savcont"><a class="savlink" href="' . RewriteLink('index.php?categoryid=' . $categoryid . '&p'.$p2_pluginid.'_articleid=' . $article['articleid']) . '">' . $p2_language['read_more'] . '</a></div><br />';
which open your article with the same number of category as p2_pluginid.
If you find a new code pls share it