This is an interesting problem.
One approach might be to switch to a Tin. Decimate it to a resolution appropriate for your panel spacing, then raise or lower tin vertices (somehow) as needed.
In the raster world, it might work to resample the raster to a coarser resolution (the resolution corresponding to the size of a panel 'parcel'. Then run 'Slope' tool on that resampled raster. You'll get a single slope value for each of the larger cells. After that, you could play with raising or lowering the coarser elevation raster to find out a version which minimizes the amount of earth to be moved (by using cut-full against the original hi-res raster, as dan suggests).
spatial analyst team