There's a guy at Columbia who is boarded in IM, EM, IM-Critical Care, and Pulmonary. He works in the unit and in the ED alternating months. He admits them at the end of the month, and is service attending at the beginning of the next.
Break the paradigm, and think of it this way: get out of the "it's 5 years!" mindset...IM/EM, you're a BC/BE doc...you do a pulmonary/critical care fellowship. You, as a fellow, are attending-level. Besides getting all the cool procedures in the Western world, you can work one to two shifts a week in the ED (you are not moonlighting, because you are BC/BE), and get all of the other coolest procedures in the world, and add $60 or $70K on top of your $65K/year you get for being a fellow (unless you are at a program that gives a PGY-6 $50 grand per year).
If you are 26, that means that, at 34, you are (hopefully) board certified X 2, board eligible X 2 more, bulletproof for academics, as rock hard a clinician you can be, and the envy of people all over. YOU say how much you want, and you get the pref over someone who 'just wanted to be a resident for 3 years'. And, lest some people not agree, 8 years is par for CT or transplant surgeons, or interventional cardiology - some of the heaviest hitters on the circuit.
It's not for everyone, but a little foresight can have you happy as all get out, and cruising way cool for your whole career.