There are "mining bonds" that are essentially cloud Bitcoin mining. As you said, they tend to not be worth buying. One exception is ASICMiner which has paid very nice dividends to their shareholders.
It's not quite as simple as selling money, since the amount of money that the box will print depends on various factors like the difficulty, exchange rate, and delivery date. So it's really a question of whether the customer's risk analysis is better than the vendor's (which is doubtful given the information asymmetry; see also Goldman Sachs). And the delivery date is definitely not guaranteed; most vendors are shipping late.
It's not quite as simple as selling money, since the amount of money that the box will print depends on various factors like the difficulty, exchange rate, and delivery date. So it's really a question of whether the customer's risk analysis is better than the vendor's (which is doubtful given the information asymmetry; see also Goldman Sachs). And the delivery date is definitely not guaranteed; most vendors are shipping late.