In a DataPilot, I want the total result column to be the sum of medians, but i can only get it to give me the median of the medians.

The data for the the datapilot is some entries for the processing time of specific products on different parts of the total process (like painting, machining...), so the sum of the medians of each of this times would give me the total processing time of the product, however I can only get OpenOffice to give me the median of all the medians.