Don’t look for Regis Philbin to retire anytime soon. ABC’s “Who Wants to Be a Millionaire,” which he hosts, averaged nearly 29 million viewers in its first five airings last week, with Wednesday’s audience of 33.6 million the biggest crowd in the show’s 36 episode history. Last week, “Millionaire” averaged nearly five million viewers more than it did in November, when it carried ABC to an unexpected victory in the ratings sweeps period. (ABC had better ratings Thursday than it had in its time slot in 17 years.) ABC is said to be considering special theme “Millionaire” shows — based on football around the Super Bowl and on movies around the Oscars. Another thought may be to bring in celebrity players.