At present it is not possible but with a small code change it can be done. Pls change the line number 116 of file framework/presentation/metabox-manager.php to
'id' => 'mo_primary_sidebar_choice',
'label' => __('Custom Sidebar Choice', 'mo_theme'),
'desc' => 'Custom sidebar for the post/page. Useful if the post/page is not designated as full width.',
'std' => '',
'type' => 'select',
'rows' => '',
'post_type' => 'fitness_class,page,post',
and then generate a custom sidebar in the Sidebar tab of theme options. Pls see the topic “Unlimited Sidebars” in the documentation to see how to set a custom sidebar per post/class/page.