Thats exactly how i did mine, but instead of splicing i just unplugged the wires from both mirrors and plugged in the NNBS wires to the 14+ mirrors.
I like the way it looks, i just dont like how straight out it looks, instead of having that curve and nice flow like the stock NNBS mirrors have.
Im still trying to find a way to mount them and have them look more like theyre supposed to be there lol. Mine kinda look funny