HI - no way to exclude form the clone, I think this is because you cannot exclude tables that are inherited from the Task table. I've been running a post-clone script to remove cases , tasks, any remaining attachments and metrics.

// clean out HR case and HR task tables
new GlideTableCleaner('hr_case', 1, 'sys_created_on').clean();
new GlideTableCleaner('hr_task', 1, 'sys_created_on').clean();

// delete any remaining attachments
  var gratt = new GlideRecord("sys_attachment");
  gratt.addQuery('table_name', 'IN', 'hr_case, hr_task');
  gratt.query();
  gratt.deleteMultiple();

// delete any metrics for HR cases or HR tasks
  var grmtr = new GlideRecord("metric_instance");
  grmtr.addEncodedQuery('definition.table=hr_case^ORdefinition.table=hr_task');
  grmtr.query();