The best way to do this without effort is to put a turbo controller with A button held down on Deadfall by Snot under the final venue in quest mode. This is a very fast vocal song that you can do on beginner vocals and use the fan trick. I both achievements without ever even using a guitar in quest mode.
IMPORTANT!- Back up your save on a usb stick before you start. Do this by going to options and saving your game, then pick usb stick as your destination. Once saved, remove the stick and go for it. This game has been known to corrupt saves from time to time if playing alot of songs in a row.
Just before attempting this go into options and hit load game, then hit the B button to cancel. Hit continue without saving. This will make it so it does not save after every song and doesn't give the game a chance to glitch. When you wake up in the morning just go back to the same menu and save to keep your progress.