Your friend is not drinking so I don't know why it would be haram for him to transport drunk people. If anything he is preventing a horrible car crash by insuring these men do not drink and then drive.
I believe asking a scholar for this question would be excellent as your friend can be in jeopardy in regards to the tahreem of alcohol in Islam and being exposed to it (even if not through drinking it and such)..it's a peace of mind