acf_custom_fields.php

<?php

function pgmb_add_acf_fields($variables, $parent_post_id){
	//Check if the ACF get_fields function is actually available
	if(!function_exists('get_fields')){ return $variables; }

	$fields = get_fields($parent_post_id);
	if($fields){
		foreach($fields as $name => $value){
			$variables["%acf_{$name}%"] = $value;
		}
	}

	return $variables;
}
add_filter('mbp_placeholder_variables', 'pgmb_add_acf_fields', 10, 2);