If you have a previous string to use to "append/prepend" the player shortcode to, you can use the Search and Replace plugin to add the [powerpress] tag. For example, search for "<!--more->" and replace with "[powerpress]<!--more-->" without the quotes (this puts the player at the bottom before the <!--more--> portion). Other than that, there's no real easy way for logic to guess where you want to put the shortcode otherwise. If you do use the Search and Replace plugin, remember to use a WordPress DB backup plugin first in case you accidentally remove something by accident and need to restore.