If this is only for certain content areas, create your own filter, and base it off the original the_content
filter.
Put this in your functions.php
(found in wp-includes/default-filters.php
)
add_filter( 'se152488_the_content', 'wptexturize' );
add_filter( 'se152488_the_content', 'convert_smilies' );
add_filter( 'se152488_the_content', 'convert_chars' );
add_filter( 'se152488_the_content', 'wpautop' );
add_filter( 'se152488_the_content', 'shortcode_unautop' );
add_filter( 'se152488_the_content', 'prepend_attachment' );
Then use the same filter. Feel free to rename it, but give it a prefix so there are no conflicts.
<?php
echo apply_filters('se152488_the_content' , $this->optionVal['custom-message']);
?>
You have to be either inclusive, or exclusive for this kind of thing, so if there are other filters you WANT from plugins you’ll have to manually add them as well.