Same concerns as has Old Smokey.
Using object code provided by others does cramp one's style for doing one's own thing ...
I have done the "put the AFM charts into the computer" thing for a number of aircraft and that gives me much more convenient control over how I choose to run the analysis.
My approach has been to do the analysis on a segmented basis, matching local slope to the sums as I saw fit, although with an eye to conservatism. Fairly easy sort of algorithms to set up ..
However, to cover my delicate little posterior for the inevitable questioning at the enquiry .. I compare the results to those obtained with an average slope and use the lesser value of the two.