Or, create a model view first, then section the model view and create a viewport of that.
Incidentally, I've found it useful for perspective or isometric sections to create both a 2d and a 3d section at the same point, then convert the 2d section to 3d and place it over the cut in the 3d section. By fiddling with the fill on the 2d section you can get your 3d section properly poched (otherwise the cut walls look hollow).