That is not currently an option in the framework. However, I believe I have a reasonably easy way for you to do it (it will be a global change though, not something that can be set per-post).
You will need to edit 2 files (they're both release specific, so the changes will stay, even if you install the
Vertex Upgrade Patch sometime in the future).
First, open {themedir}/theme-globals.php and make the following changes:
On line 95, change:
$s5_loop_tags['thumbnail'] = '<img alt="%post_title%" style="position:relative;float:left;padding-right:10px;" src="%thumb_path%" />';
To:
$s5_loop_tags['thumbnail'] = '<img alt="%post_title%" style="position:relative;float:left;padding-right:10px;" class="post-thumbnail" src="%thumb_path%" />';
Then, open {themedir}/style.css and add this to the bottom:
.item-page img.post-thumbnail{display:none !important;}
Those changes will make the Featured Image (Post Thumbnail) be hidden on any "single" view for a post or page.
[Note: I am moving this topic to the correct board; please remember in the future to post theme/plugin specific questions to the board created specifically for the theme/plugin you are asking about.]