Hook to page, without creating menu item

Hi,

I want to hook function and retrieve the page-hook (hook_suffix), but without creating a menu item.

I now have this line
$roxal->project_edit = add_submenu_page( 'roxal', esc_attr__( 'Edit project', 'roxal' ), esc_attr__( 'Edit project', 'roxal' ), 7, 'project-edit', 'roxal_project_edit' );

This creates a submenu. Is there another way to get the hook_suffix in $roxal->project_edit ?

I tried with add_action, but that only returns a boolean….