Hi!
Only with a minor modification to the code, there is not other way unfortunately.
If you open up the wp-content/plugins/ajax-search-pro/includes/search/search_content.class.php file and scroll down to line 607, where you should see this:
[code]ORDER BY priority DESC, relevance DESC, " . $wpdb->posts . "." . $orderby . "[/code]
change that line to:
[code]ORDER BY RAND()[/code]
That should do it.
Please not that this solution is not update-proof, so once you update, you need to do this again. Also, make sure to do tests with a few phrases, random ordering might be a resource-heavy operation in some cases.