My understanding on Gem blades in the V2 Genesis were as you described. However I just had to give it a try and see for myself. I can say that I used a Gem blade with only the spine removed in my Genesis V2 today without any issue. As you noted it does not lock into place however the friction fit was tight and the blade did not have a smile. I have no problems getting good results with the Feather blade. The shave with the Gem blade this morning was a good as the shaves with a Feather. I will continue to use the Gem blade next week to verify the results.
Yes could you keep us updated on how the shave compares using the Gem vs Feather. If the shave is better in the V2 with the Gem blade without the spine I'd like to try it in mine. Honestly I have never taken the spine off a blade before and I'd like to find out the best method of doing it without damaging the edge.
Thanks