B737-400 Captain reports failure of load planning to provide accurate takeoff data for a takeoff with a PMC deferred inoperative.

Narrative

With the right hand PMC deferred inoperative; an increased max power takeoff setting is required. The performance manual does not provide PMC OFF Data. Under the heading of MEL/CDL the takeoff data that we received indicated 'NONE'. The available power settings that were provided for Flaps 5 reflected other power settings that were not in compliance with the MEL procedure and none that provided the setting required. This left a window open for a crew to use the wrong power setting for the MEL issued. When we noticed the error we contacted Dispatch and informed them of the error; they said that there was no way to put a MEL/CDL adjustment into the takeoff data computation; yet; there is a header for such info. When we tried to pull up the V Speeds on the ACARS T/O DATA feature it would only provide V Speeds for improved climb. We were 23;000 pounds under our release weight and at 101;000 pounds the improved climb speeds were 40 KTS faster than what would be considered normal for our low weight. It would be difficult to keep the aircraft on the ground at such high speeds and thus be unsafe. The dispatcher did not have a solution since 'the data was all computed by the grave yard shift.' I suggested that the duty flight manager be called and that the info should be available if engineering was contacted. The duty manager agreed and we received the correct data 59 minutes after our push. This happened again on the next leg as well. Interesting to note that on that leg when we contacted Dispatch they said; 'Yeah; we figured you would be calling' insinuating that they were aware of the issue yet had done nothing to correct it and just waited for us to contact them. Dispatch said that they would send the data to airport operations and have them bring it out to us but we offered to take it verbally over the radio; which they did. On the last leg we did get the correct data for but it was provided along with the additional runway section not the 'preferred' runway section; once again leaving a window open for the wrong data to be used if a crew missed it. The supplemental procedures in the flight handbook or MEL procedure doesn't mention that the Thrust levers may have a 1 knob plus split with the PMC inoperative. Because of this an unneeded log entry was made adding to our delay. All in all the system that is set up cannot be depended on for a safe operation with this MEL. We have been told by flight operations that we the flight crews are the last line of defense. It is becoming more apparent that we; the flight crews; are quickly becoming the 'ONLY' line of defense.