Again,
I have no great insightful words to suggest in an intervention.
But from what I have read of interventions, the key for the participants is to speak about how the person's addiction has hurt them and that their only wish is for the addict to find sobriety since they can see it destroying the addict.
It is best if there is a rehab already on notice that the addict may be coming. A professional interventionist will have a rehab alerted and be ready to transport the addict as soon as he / she agrees to go --- "strike while the iron is hot".
Keep coming back,
Jim