Start by explaining how you did working days only. I'm assuming that holidays are not working days. I'd bet you find the answer in what you originally did.
So, let me give you one (of many) possibilities. You write an abap the schedules jobs to run imediately. It only does so if today is a holiday, else it exits. You then schedule it every day. I posted a document somewhere telling how to write the code for scheduling a job. I can dig it up if you'd like.
Neal