THE DIRECT ROUTE: Filmmaker Kevin Smith (‘Clerks,’ ‘Dogma,’ ‘Mallrats’) tries his luck as a radio show host today (3/3) — a job he knew nothing about just two days ago. While Kevin was doing an interview Tuesday with San Francisco radio station Alice 97.3 to promote his March 28 Vulgarthon 2005 film festival at Hollywood’s Arclight Cinerama Dome, one of the regular co-hosts asked Kevin to replace their other host while he is on paternity leave. Without hesitation, Kevin agreed and soon set plans to fly to S.F. yesterday to take on the fill-in job the rest of the week.