An airline with which I am familiar has its own rule that demands that if a crew member flies as a passenger on his own behalf before a flight then the full duty rest period must be taken before operating a flight duty period, i.e. you must be within 1 1/2 hours of the place of reporting for twelve hours before the flight.
A junior manager has the bone crushingly boring job of scanning all staff travel receipts each day to compare them to the rostered duty to ensure compliance. His only pleasure is when he finds a culprit and can get them. Some pilots and cabin crew have been sacked for this, even though they rested well as a passenger on the incoming flight. Paying full fare on another operator works, but there is always someone ready to dob you in if they see you at the airport.
Yes, it restricts commuting greatly but it does prevent that 1% of pilots from abusing FTL's and arriving tired for work.
Oh, and Lanfranc <What someone does on his own time, off duty, is NO business of yours or the company for whom he works.> is not true. A company may have no right to control what you do in you off duty time, but many do, both inside and outside the industry.
As an aside I often wondered why if I take the ferry from Macau to Hong Kong (one hour journey) to get to work I am OK but if I take the helicopter (14 minutes) I am in breach of company rules? Such is the silliness of a power and control bureaucracy.