The closest I could come up with in an approximation is a combination of Grid volume and Generate ISOPACH. There might be another step or a different command then ISOPACH, but you can plot cut and fill text in a grid and even color code the cut and fill lablels. These represent the height of the grid prism used in the grid volume. I even new people who copied these into Excel to compare InRoads Grid Volume to the Excel volume using this method.
Also, if you use a tighter and tighter grid, the grid volume gets closer and closer to the triangle volume. It just takes a lot longer.