line 2651 of PiePlot.java in drawSimpleLabels() should be something like:
RectangleInsets labelInsets = this.getSimpleLabelOffset();
Currently has hardcoded default values, which produces the bug that simpleLabelOffsets set in the plot are ignored.
Compiled and tested, seems to work.
An additional method to position the simple labels (which I would use;) would be to specify a distance from the center of the pie chart to place the labels. That is, the center of the label would intersect a line drawn from the center of the pie chart outward through the center of each section. All you'd need to specify would be the distance.
Also might be useful if you could supply an array with offsets (or my proposed radii) to position labels in each section.