Simple. Pick a date at least 5 years but no more than 30 years from now. Work out some goobledegook reasoning on how this might be THE DATE for the end to come. Lay the groundwork slowly and subtly, a study article here, a convention talk there. Of course, never directly state anything that can come back to haunt them later. By 2006 you could have have some momentum going.
Will this work? Will people be dumb enough to fall for this again? Of course!!
No Apologies ( of the maybe I'll start my own religion class)