I was about to take a cutting wheel to the cheapest flat head screwdriver I could find in my toolbox, but then found a sort of "purpose-built" tool that should do the job equally well. It's a cheap spring bar tool, made in China and available off of Amazon for a few bucks, intended for use on watches and watchbands. It has a notched flat head on one end. I'll report back on it after the next time I detail strip my P-07's frame, which will probably be after my next trip to the range.
This technique of hooking the spring prior to snapping the decocker together, I may try that too, but I expect to fail at it... it's a mild struggle for me to get those parts lined up and snapped together, which I always succeed at pretty quickly, but to keep that spring in place at the same time, sounds like a frustrating exercise.