I’m always surprised by the creativity of the community; I never would have thought to use a radial texture for this. I’d also never used the Build Modifier before so this was a pretty useful exercise.
I found another solution which is to apply a Curve Modifier (using a Bezier Circle as the curve) to a Cube, and scale the cube along the axis of deformation. Just be sure to apply a fair number of loop cuts to the cube mesh to give the circle a good resolution.
I implemented these three different approaches in one .blend and animated them for future reference, if anyone is interested.[ATTACH=CONFIG]141228[/ATTACH]
pie_graph_methods.blend (468 KB)