You can do this fairly easy and you don't have to wrack your brain over it. Simply play co-op with a friend and at the begining of the first level die and lose all of your lives and then let your friend continue on without you until he beats the last boss in his final form then you mooch one of his extra live off of him and then both of you jump on to the helicopter.
This can be done for the "innate guerilla warfare" achievement as well. The only problem it that it takes a lot of time and your friend has to have an above average skill in the game, in my opinion.
the reason i wrote and don't have the achievement is because My friend and i were on the final boss and then my router failed and i lost the heart to sit there and do it for another few hours. Despite that, this has been confirmed by a few of my friends that have done it.