Well assuming I understand what your asking, I don't V and then Y. I just Y. I usually make my own cables so I don't have issues of removing one wire from the crimp connector, but I have used the existing wires for a Y connector in the past. Here's what I did:
I took the double wire and where there is the single crimp for 2 wires, I spread the wires apart from each other as far apart as possible up to the crimp.
From there, I took an xacto knife and cut the wire in front of the crimp contact "wings"(ie the things that bite into the plastic part of the wires). This cut is below the pins, so that the pin wires inside the pin is not moved. This maintains the strength of the pin as the wires have not been moved and therefore the pin is still biting into both wires with one wire being cut and the other being untouched.
With this done, I measure the length I want the Y to occur at and from there strip the wire as highlighted by this guide.
Mind you, some people say that its ok to open the crimp slightly and from there remove one wire and use a pliers to close the crimp back over the remaining ONE wire. I have done this in the past and I must say that many times in closing the crimp using the pliers, you can either damage the crimp or you can find that the crimp no longer holds the wire securely. Hence I'd suggest yo just cut the wire.
Some might also say that by cutting the wire, you have part of the wire still in the crimp with current passing through and there is a risk of shorts or shock etc. But I say to you, in sleeving, you will be covering this supposedly "exposed" wire with sleeving and in some cases even heat shrink, so there is no risk there.
Hope I've been helpful.