Physiotherapy management and drug abuse

How do other Physios broach the subject of drug abuse with patients?
I feel this is a pertinent issue in both the outpatient and inpatient setting where my skills are inept.
I have recently had a patient with a 20 yr Hx of LBP from a stab wound who displays all the signs of IVDA however reports to me that he is on methadone.
The implications for my treatment are as follows;what is his motivation for physio, he can't take other analgesics, other modalities such as acupunture will have little impact due to his altered pain mechanisms.
My aim is to achieve function as appropriate. Do other physios have training in this area?
this problem isn't so relevant in private practice however, i work in an area of social deprivation where this is a common problem.
Thoughts appreciated
Laura