The is easiest to do by exploiting the broken talkie system (where all talkies register 100% to any noise).
Log in your main profile for which you want to get the achievement, pick guitarist\bassist\drummer, then log in a second player as vocals. Then, go pick the "Talkie Challenge" (which involves Give It Away, So Watcha Want and Testify) and place the microphone up to the TV's speakers and it'll 100% everything without the player providing any input. Play guitar\bass\drums as normal.