you can do this by editing bfa_post_parts.php and fine line 122 (in version 3.4.6) which is
HTML Code:
the_content($bfa_ata_more_tag_final);
and change it (actually you just add a line before it) to
HTML Code:
if ((is_page()) and (function_exists('the_post_thumbnail'))) the_post_thumbnail();
the_content($bfa_ata_more_tag_final);
this will cause a thumbnail to show on a page