I tried the grating method today for Sunday lunch, and it was much more successful than I expected. I grated a potato for each person and submerged the grated potato in cold water. This washed out a lot of starch. I changed the water twice, swirling the potato round until no more seemed to come off it. The I tipped the strained strands into a tea towel and wrung them out to get as much liquid off as I could.
I added about half a grated onion, one egg (for 4 medium potatoes) and seasoning, then fried it in a cake about 1/2 inch thick. I ate a quarter of it - ie one potato's worth, with steak and vegetables, followed by mixed berries and cream. My pre-lunch level was unusually low at 4.6, which I was a bit surprised about because I had eaten a crumbed chicken leg at a buffet about an hour before. 1 hr after the lunch, I was at 6.4; but at 2 hrs I was higher at 7.0. However, by just less than 3 hours I was down to 5.7.
So although it had more impact than the juiced potato, the grating and washing did make a significant difference and would definitely mean that this was something I could eat. My kids loved it too - I didn't tell them it was reduced carb<g>.