XCode 7.3 и Swift 2.2:
let event1 = CGEventCreateKeyboardEvent(nil, 0x09, true); // cmd-v down
CGEventSetFlags(event1, CGEventFlags.MaskCommand);
CGEventPost(CGEventTapLocation.CGHIDEventTap, event1);
let event2 = CGEventCreateKeyboardEvent(nil, 0x09, false); // cmd-v up
CGEventSetFlags(event2, CGEventFlags.MaskCommand);
CGEventPost(CGEventTapLocation.CGHIDEventTap, event2);
Код выше имитирует CMD-V, затем отпущен (AKA: paste).