Crowdfunding campaigns often rely on perks to entice people to contribute. Usually, it’s stuff that’s not all terribly interesting – a signed copy of something or other, or worthless swag like a bumper sticker or ballcap. But Radius Ensemble, the chamber music founded by oboist/impresario Jennifer Montbach, is offering something better. The group, which gigs four times a year at the Longy School of Music of Bard College, is raising money to finish a CD, “Fresh Paint,” featuring new works by composers Elena Ruehr, Jonathan Bailey Holland, Eun Young Lee, and John Harbison. For small-sum contributions, you get a CD or a digital download, but pony up $2,500 and you’ll get to play Rock Band with Eran Egozy, the MIT alum who cocreated the wildly popular video game. “How cool would it be for you and four friends to play Rock Band with Eran Egozy?!” Radius Ensemble raves on Indiegogo. But, wait, there’s more: Light hors d’oeuvres and drinks will be served while you play.