This achievement is most easily achieved at the beginning of the game, before any additional islands have been unlocked. First, get on the train tracks that go under the Algonquin Bridge. The easiest on-ramp is on the eastern side of the island, near where you find your cousin Roman in the mission "Bleed Out." Once on the tracks, head west towards the middle island. Provided you have not yet unlocked the island, when you get about halfway across the bridge, you will receive a 6 star wanted level. However, you are safe here because the police cars and helicopters cannot get to you here, however, swat team climbers can. So take your time, continuing onto the second island will bring you into the underground subway tunnels, again, where the police cannot find you. Once 5 minutes is up, and as soon as your wanted level goes away (either by dying or by evading) the achievement will unlock.
Another way is get a helicopter (before you unlock all the islands) and then just fly over onto the second or third island and then you will get a 6 star wanted level. Then you just fly around for 5 minutes.
Gotten from the xbox360achievements.com guide.