First, he should be able to cancel even if it's in production.
I've made & subsequently cancelled lots of orders, many while they were in production.
Second, if he doesn't get it cancelled before it ships, he needs to refuse shipment. If it's successfully delivered things will get MUCH more complicated.
Third, if it is successfully delivered he needs to call Dell & return everything for a refund (within their grace period, it used to be 30 days... Could be different now).
He will be responsible for return shipping in #3, it is MUCH simpler to have it refused.
Viper GTS