This will be most useful in cases where your documents are standardized to have the same predictable artboards, or artboard-areas of sorts. What you can do it put a series of guide rectangles (not really guides) so that you can select each one by note and set the active artboard to it's shape by Fit to Artboard Artwork Bounds command. Then you do the export and activate the next rectangle to fit the active artboard to it. You could also have it come all the way back around to reset the original artboard. However this will only work if you ensure to start on that artboard as active, first.
Also you could lay down paths with the rectangle tool, etc, or a shape with "Insert select path" flyout command in the Actions panel. Then you can use the command to Convert to Artboard, and you'll have one extra artboard which is then moved around but a script will need to delete it.
However if you plan on doing the exports and not saving the document, you'll be able to simply get away with having the guide rectangles and selecting each one and converting each one to a new artboard so it becomes the active artboard and you get double the artboards with pairs one on top of each other, which for exports should be not an issue. Then when you close the document without changes it's all good since all the new-created stuff goes away..