I don't think you would be able to get a refund. I believe they would IDB someone before giving a volunteer a refund on their ticket... plus IDB's in general are pretty rare and it is much more likely there will be another happy volunteer that will accept whatever they are offering.

You can ask for travel credits in lieu of a free ticket... usually you will be successful in doing this but there are GA's out there who won't do it because they either don't know how or they don't know that it's OK for them to do so. But the amount of travel credits are awarded based on how long your delay is.