OK, just had an idea. Some pages without comments are short, too short to have many ads on a side bar. But then when they get some comments, they are long.
Is there a way in Wordpess to add something to the bottom of the sidebars (in the template files, or plugin, preferably in template files) that says (in WordPress/codey language stuff):
"if there are more than 5 comments pop this advert here"?