Thanks for the suggestion. Unfortunately, I can't figure out how to get what I need using the expand tool. What I'm trying to do is add orthogonal cells to diagonally adjacent cells so that I don't have any cells that are only connected diagonally.
I figured out that if I convert the raster to a coverage, and then back to a raster, it adds those orthogonal cells in during the conversion. This is a satisfactory solution. I am curious though why this does not work if I convert it to a polyline and then back to raster.