You can also layer the spray starch. A fan helps speed drying between layers. I doubt the spray starch will be as strong as liquid starch, even if you saturate, but it might be enough. If you think about it, when you dilute Sta-Flo you dilute it to different strengths. Spray starch has to always be a lighter starch solution simply because it has to fit through the spray nozzle. But, worth a try.
Incidentally, many grocery stores also carry Sta-Flo. Look for it in the laundry area, usually on the most bottom shelf.