Reporting barrel purchased by customer?

[Longdogs]

I've got a customer that wants to pay for a barrel of bourbon now, let it age here and have me bottle it when he feels its ready.  I see other distilleries offering this type of thing, but I am not sure how to deal it on the TTB side.  Do I just give him a receipt for x amount of bottles to be picked up at a later date and treat it the same as all my other barrels?

[Jedd Haas]

I haven't done this yet but have thought about different methods.

One idea is to structure it as an "exclusive right to purchase" the finished bottles. The customer can then pay you a deposit. For example, 99% of the final price. That way the barrel is still technically yours and no reporting would be needed. They can then pay the final amount when the barrel is dumped, bottled, and the bottles are withdrawn.

However, are you allowed to sell an entire barrel's worth of bottles to your customer all at once? This will vary by state, but this problem will only arise when the spirits are withdrawn.