Enroute Controller described a confused emergency operation when the Supervisor was issuing instructions to the reporter that were counter intuitive to handling the subject type of emergency.

Narrative

I [handled] an emergency going direct to the airport from the west. When I sat down at the position the relieving Controller told me that everything had been passed on to the TRACON and it was all ok. When the plane was 20-30 miles from the TRACON boundary the Supervisor told me that I needed to clear him direct to the airport for the approach; which is what the pilot requested. I said that it would put the aircraft 50 miles out of the way and not a good thing for a plane with one engine. I told the Pilot what they wanted me to do and said I'd try to get them pointed in the right direction; but not too far out of the way. I called the TRACON and asked if they had been told the same and they said yes. I told them I thought that it was too far out of the way and approval requested a heading; which they approved. I turned the plane left and when the TRACON took the hand off I gave the Pilot the frequency change. While this is going on; the Supervisor is telling me the plane needs to go a different direction. After I shipped the plane I told the Supervisor what I did and everything had been taken care of. Recommendation; Supervisors should know what is going on instead of just blindly doing what others say. A good supervisor would not have said to turn an airplane with one engine out of the way.