You can fly with first initial, last name (at least for a little bit longer). If you did something elaborate, I'm sure you could pull it off.

That said, people have been caught. And now that the airline will be collecting ID info with birthdate and all for domestic flying, it'll be much easier to get busted on something like this.

Also, with continuous improvements in data mining and analysis, it's getting easier and easier for airlines to catch this stuff. There was a story on the DL board a year or so ago about DL crunching through old flight data and catching people on this. All it takes is a mistake -- one family member flying LAX-EWR while another flies IAH-SEA within an impossible amount of time, and they got you, and the records to prove it.