My problem with this is that I can't do the curved surface projection in my head accurately. I can draw my sketch on the tangential plane, but I have no idea how to dimension and distort it, so that when it gets wrapped around the cone, it will constitute exactly one half of that cone. With this method it seems that I'll either have to do A LOT of trial and error and then end up with an inaccurate model, or I need to do some 3D geometry transformations on paper so I can calculate the exact parameters for the sketch. Both seem like a lot of work - there's got to be a better way!
Another idea I have is to somehow "unwrap" my cone, sketch on the unwrapped version and then wrap it back into a cone. Maybe the Sheet Metal module in SW can help here?