Buy all the entourage members that increase your fan percent. You will end up having thousands per song. Then just keep playing songs. It won't happen fast but won't take too long either. If you get stuck, keep playing the Rock Power Challenges. These give 3x fans, plus any extra bonuses you get could net you 40,000 in a song. Playing a three song set with the first two Entourage multipliers on, on Expert and getting five stars earned me 80,000 fans. It really depends on how you play and how good you do with the setlist.