I learned to fly instruments in a TH-13, with no stability augmentation at all, and while I wasn't actually single-pilot, I may as well have been, because the instructor in the left seat wasn't helping, only observing and occasionally criticizing, sometimes loudly. We had to plan and fly the approach alone, every time, as well as plan and fly holding, etc. Flying instruments in the UH1 was a piece of cake after that, being more stable and having someone to actually help in the other seat. It doesn't take that much time looking at the approach plate if you're used to it and know what information you need at the moment, and where it is on the plate. Helicopter SPIFR isn't easy, but it's certainly not impossible.