VDB is a reverse auction in which the dealer knows what everybody has and the dealer is DL. In theory, DL should be thrilled to pay in miles rather than a voucher because the miles simply devalue redemptions and ultimately lead to increased redemption amounts to get them off the books, but it doesn't work that way.

If the GA offers a voucher + room + food vouchers and you want something different and there is someone else standing there who takes what the GA offered, you are SOL. If you are the only taker, it's then time to talk.