Well, my technique is to use 45 degree long needle nose pliers and grip on the clamp itself while twisting and pulling. After the clamp just begins to get on the nipple I then grip just behind the clamp while pulling with a bit of a twist. I never attempt to directly spread the clamp instead I just let the intake nipple do it.
Well, sometimes it's twisting, pulling and cussing!
I also slick up the plug with the spit de jour. Makes it easier to slip over the nipple.