From the 'Golden Arm', which is what I call the position when you are in Half Guard with the Lockdown and you have your opponent's far arm trapped in a 2-on-1 grip, you can easily transition to their back to sink in the RNC.
Once you Whip Up to your side with Double Underhooks there are a couple ways that I use to trap the persons far side arm. One is to grab their wrist and snatch it into their body and get the 2-on-1, or "Golden Arm."
The way that I do it in the pictures below is to do a little Chi Sao by keeping the arm over your opponent's back ready to grab the 2-on-1. Your other arm strikes their supporting arm outward and back passing it to the arm over their back.
Sometimes, in the middle of the scramble, you just find yourself with the 2-on-1 from the Half Guard with the Lockdown.
Once the arm is trapped you can also go for Old Skool or the Electric Chair with variations if they get the Whizzer in. You can check em out here:
From the Half Guard with Double Underhooks and a Ball & Socket Grip you first ...
Whip Up to your side. I like to maintain the double underhooks to control my opponent's posture as I raise their leg and my arms up toward my head.
The double underhooks are important because they help to stop the Lockdown counters.
Once you get to your side you want to squeeze your grip into your opponent's floating rib to maintain good control.
Next you do Chi Sao by striking your opponent's arm out and back with your forearm while maintaining a tight hook across their back with your other arm.
Then you pass their arm to your other arm so that ...
You can get the 2-on-1 aka Golden Arm. Once you have the Golden Arm you want to keep the arm over your opponent's back tight so that they cannot get a Whizzer in. If they get a Whizzer it stops the transition to the back. There are other techs you can use to deal with the Whizzer that you can find at No-Gi-Grappling.com.
If the Golden Arm is tight your opponent will not be able to get the Whizzer so their only grip will be to grab your head as in the last pic. All you have to do is go out the back door by shrugging your shoulders and popping your head out.
Now the path to the back is wide open.
From here you let go with the arm that is on the mat and you go for the RNC while keeping your opponent's arm trapped with the other arm. At this point you can let go of the Lockdown and ...
Get your hook in as you grab your opponent's shoulder blade to set up for the RNC. Then you ...
Lock in the RNC with both hooks in. It's best to put an Anaconda or Body Triangle on at this point to help you stay on their back. Of course you want to be flexible enough to switch your hooks if the person tries to roll to the other side in order to break your Anaconda.