This is probably one for a lawyer or accountant, but the source of the money or other thing of value that's contributed isn't an issue. It doesn't have to be "income" to be deductible. My concern would be with attaching a value to the miles. Two cents a mile seems to be sort of an airline industry standard, but I'm not sure the IRS would buy that. Then, you're opening the door to an IRS evaluation of the miles you earn as income, based on the same value you placed on them as a deduction. I'd stay away from taking a deduction.