Elstein has been hired officially by Luther Pendragon Holdings, the vehicle through which the MBO was undertaken.
Elstein said he would apply his 'experience in mentoring management, shaping business plans and helping small organisations to grow'. He said the role would demand a day or two of his time per month.
Luther partner Daniel Guthrie said: 'David is outspoken and challenging, traits that fit well with our culture.' Elstein used Luther in the past to handle his Broadcasting Policy Group report on the future of the BBC.
Before launching the then Channel 5 in 1997, Elstein was head of programming for BSkyB. He currently juggles seven other chairmanships, including the Commercial Radio Companies' Association and the British Screen Advisory Council.
Luther partners Gina Coladangelo, Amy Kroviak, Simon Whale and Guthrie bought out founders George Pitcher and Charles Stewart Smith for an undisclosed sum on 30 November 2005.
Since news of the MBO emerged, Luther has been hit by the departures of associate director Susie Winter, who last month joined the Alliance Against IP Theft, and partner Douglas Trainer.