You can try some potentiation techniques. For instance using cimetidine and/or white grapefruit juice can inhibit it's metabolism to the less active metabolite noroxycodone. Or you can use other substances to boost the effects like analgesia and the nodding. Drugs like sedating antihistamines (hydroxyzine, diphenhydramine), non-narcotic pain relievers (acetaminophen, ibuprofen) and muscle relaxers (carisoprodol, tizanidine) all can do this. Benzodiazepines would also work this way, but are kinda dangerous with opioids so wouldn't recommend.