It’s strange that wpthemedetector is detecting something elase as wordpress theme you are using. The following steps should help.
I have added following line in “replace in HTML” option box under general settings tab:
wp-content/uploads/=file/
and following line in “replace urls” option box”
/wp-content/plugins/userpro/skins/elegant/style.css==mycustomstyle.css
Now goto http://leprodtest4.wpengine.com/wp-admin/options-general.php?page=hide_my_wp&nginx_config=1 and add the rule “rewrite ^/mycustomstyle\.css /wp-content/plugins/userpro/skins/elegant/style.css” in WPEngine panel (it should be the first rule in WPEngine as well)