First, no handcuffs or zip-ties! For Police Officers, if they don't have a partner to assist, handcuffing a suspect is probably the single most dangerous moment of the encounter. Why? Because you have to get up close and personal to do it. At a distance of only a couple of feet, your gun can become more of a liability than an asset. As an untrained citizen operating alone, attempting to apply a physical restraint can be an invitation for the VCA to take that pistol away and, at best, turn the situation into a ground-and-pound.
We had a thread a while back about the worst firearm gaffs in the movies, and I don't if anyone posted, "Anytime the guy with the gun walks up to another guy in order to stick the barrel of the gun to his head, face, chest, etc." Though admittedly risky, it isn't difficult to remove a gun from someone's grasp if the gun is close to you. You don't want to go there. Use the defensive distance the firearm gives you.
Second, holding a VCA at gunpoint is not a preferred outcome, but may be inevitable. As others have said, if he tries to run, don't stop him. But if you have to hold him, know how to position the perp: face down, legs spread, arms straight out and palms face-up. Whatever side you choose to move to, have him turn his head to the other side. A good option is to position yourself no closer than 15 feet away, and between 135-145 degrees from the line-of-sight of his turned head. That way, he must turn his head all the way over in order to see you, even in peripheral vision, but you still have a decent view of his line-of-sight.
Third, work on your command voice. Your handgun alone may not be all that intimidating to an MS13 member. His perception of your willingness to use that gun, and his perception of your experience doing so, may well be more important than the gun itself.
Fourth, worry more about yourself than the VCA. The sirens are nearing, and you can see the lightbars flashing. You're positioned behind the VCA's sphere of vision, and he's been compliantly lying spread-eagle.
Holster your gun. Do not have a gun in your hand when the Law Enforcement Officers arrive on the scene. Do not drop the gun to the ground (wouldn't that look a little guilty to you?); holster it before they arrive. If the VCA senses this and runs away, so be it. Ain't a bad outcome.
Extend your arms fully to the side and in front of your shoulders, a little above shoulder level, and spread your fingers; not the hands-above-the-head "I surrender" posture.
"Thank God you're here. I'm the one who called."