That's a good question which I hadn't thought about. If it were me I would probably create some kind of a membership card and then personally try to make the sale (or train someone to do it). Just the simple, "Oh you'd like to buy an album for $14.99? We have this option here as well, it's a much better value, etc, etc... interested?" I'd probably throw in a physical album as well so they got to walk away with something and then I would tell them the registration info will arrive via email within 24 hours. But you would need a credit card processor to make that work.

With that said, I think it might be a bit of a tricky sell in a live show situation unless you already have a dedicated following, but I may be wrong on that. Simply because the payment processing procedure would be an unknown to them and ultimately I think buying a digital product online is just easier to digest for most people.

But I'd be interested in hearing if you have some success that way.