Prevent block from being used in main editor, use only as inner block

I am currently using the allowed_block_type filter to control the available blocks in my theme, similar to the following example:

function acf_allowed_blocks($  allowed_blocks, $  post) {     // Register core blocks     $  core_blocks = array(         'core/buttons',         'core/heading',         'core/image',         'core/list',         'core/paragraph',     );      // Register custom blocks     $  custom_blocks = array(         'acf/test-block',     );      // Register plugin specific blocks     $  plugin_blocks = array(         'gravityforms/form',     );      // Specify block groupings available on specific post types     switch ($  post->post_type) {     case 'post_type_example':         $  allowed_blocks = array_merge($  core_blocks);         break;     default:         $  allowed_blocks = array_merge($  core_blocks, $  custom_blocks, $  plugin_blocks);     }      return $  allowed_blocks; } add_filter('allowed_block_types', 'acf_allowed_blocks', 10, 2); 

While this works perfectly, I am trying to determine whether or not it’s possible to remove the gravityforms/form block, but allow it inside the acf/test-block. Currently, if I remove the block from this function, it’s also becomes unavailable as an inner block in my ACF block markup, which looks like this:

$  allowed_blocks = array( 'gravityforms/form' ); echo '<InnerBlocks allowedBlocks="' . esc_attr(wp_json_encode($  allowed_blocks)) . '" />'; 

Does anyone have any idea on whether or not this is even possible with the current state of Gutenberg? I can just as easily live with it being available as both a main and an inner block, but it would be my preference to only use it as an inner block.