Let's get one thing straight: there is *no* online community for this game. However, luckily for you, EA doesn't own this game. That means that it's still possible to get it, even if you have to bribe someone to do it with you. The other alternative would be to have two Xboxes.
Assuming you *can* find someone, all of the online achievements can be boosted in 20 minutes. For this one, load up Head-to-Head and choose Ranked, one song. For faster results, set the instant knock-out on, so that one player can lose by not singing. You can choose the Short mode if you like. Both people need to play the whole song to count.