At breakfast on Thursday she bored them all stupid with flying tips she'd gotten out of a library book called Quidditch Through the Ages.
I guess that one possible name for stupid is a "resultative secondary predicate". A resultative secondary predicate describes what state the verb's argument has assumed as a result of the event expressed by the verb:
Stan cooked the steak black
Boris pounded the metal flat
She bored them to a dazed, "stupid" condition.
In the parlance used by Huddleston and Pullum, stupid is not an adjunct either. They write:
Obligatory predicatives are clearly complements, dependent on the occurrence of an appropriate verb. With optional ones, however, there are grounds for saying that while the resultatives are complements, the depictives are adjuncts. (Chapter 4, §5.3, "Optioinal depictive predicatives as adjuncts")
In your example sentence, stupid describes the result. It is not depictive. In H&P's terminology, it is an "optional resultative predicative complement". It's object-oriented: its predicand is "them (all)".