You can do it by padding your 2D photo out to a 360x180, then restricting the parameters (auto, fovmin, fovmax, titlmin, ...) to show only the part that is your original photo. That means messing about with the file after PTViewer Scripter has created it.
Handcoding PTViewer scripts isn't much fun, but it can be done. With my fumble fingered typing I was never able to get much to work with PTViewer until I bought Easypano's Scripter. Making modifications to that output is *MUCH* easier than starting from scratch.