You've got a job ahead of you. I run a Kato and I have experience with my gf's VTR. Strangely, I run my Kato regulated (kicked).
But ... here's a stab at a description of what's happening to bring the positive terminal to the top cap center pin. At the bottom of the battery tube, there is a metal bar which transfers current to the atomizer side of the mod. It is insulated from the body of the mod, and the center pin is a long copper screw which is threaded into the bar. I run my Kato with the positive pole facing the bottom of the mod which makes the body of the Kato my ground connection by way of the fire button. For my purposes, I replaced the long copper top cap center pin with a kick on the atomizer side of the mod.
HTH