Sorry, I don't think there's currently a way to copy multiple frames at a time. The way it should work is if you select multiple main-line key frame nodes in the time line and just press control plus C, then move elsewhere and press control plus V it should paste copies of the frames you copied starting at where you now are on the timeline, BUT I just tied this and while it seemed to work, the frames were all the same instead of reflecting the actual frames that had been copied/
I'll report this to Edgar and see if we can get this fixed or implemented, but I can't guarantee how long it will take.