Auto-responder in Outlook 2007 a la 4-Hour Work Week

I am trying to set up an autoresponder in Outlook 2007 that notifies
people who have not emailed me before that I am only checking email
twice a day.

So far, I can't figure out how to do this. I can set up an out-of-
office notifier, but it says "Out of Office" in the subject and will
basically autorespond once a week. Or I can set an autoresponder that
notifies everyone every time they send an email. Neither option is
attractive.

Does anyone have a suggestion?

Thank you!
Publius74