As you mentioned in your intro, this is a not merely a pattern, but a tactic of the left. It is an extension of the seminar caller. They are told to feign being former Republicans, military etc. because that gives them more credibility to attack the Bush Administration. Now that tactic has bitten them in the butt. I had one on another internet site who claimed to have been a transgendered Colonel that had just been promoted to General. She even e-mailed forged promotion documents. What a loon!
Yeah, these fabricated leftwing stories are happening with ever greater frequency. Hey, remember that leftwing professor in Kansas or somewhere in that neighborhood who claimed that some rednecks tried to run him off the road? BTW, among the biggest practicioners of leftwing fraud are college profs.
Another common scam is when the media presents some "average" housewife who has "progressive" views and then it turns out she is a hardcore leftwing activist loon. I see that a lot. Remember the "average housewife" who organized that Million Mom March? Turns out she had worked as a producer for Dan Rather.