We did a Sandy Relief benefit last December, with a local collective of artists and DJ/Producers. Granted, we had a lot of "art objects" (paintings, DJ mixes, music tracks, digital art pieces, etc) that were donated by those who created them. We had a Silent auction the night of the event with the works that were physically at the event, but also hosted digital images on a website that people could view (which allows people not physically at the event themselves to view and submit bids by email, etc.).
You would probably have to discuss the logistics of the online aspect of this with someone affiliated with your group that had some basic technical proficiency to do this). The gist is you have a deadline date and a bid expectation, the great thing about art objects is that people will value them differently and it is entirely subjective) that people at the event can bid on as well as online viewers, with the item in question going to the highest bidder. We also hosted a catered buffet the night of the event, which tickets were sold through via Eventbrite. People could view the art, eat dinner, and rock out to musical performances, real classy like... then buy the music they were experiencing. i think many were impressed with our presentation (was also done in conjunction with a local Church, in the basement) so we were able to sell it within the parish community, as well as just people interested in our efforts.
The link below was the program we used at the event, just to give you an idea. I'll go further in detail into this if you PM me or something, I'm a bit drinky at this posting
but thought it might at least give you some food for thought.https://docs.google.com/file/d/0B_qAnTH1AWHAYzZiZGMxRG0wZGM/edit