I happen to have the same stove as you, actually I have a 48 RNB I bought 4 years ago, I believe they have done some redesign since then. Preheating underneath the broiler has not worked well because it doesn't stay on long enough to properly heat the stone (30-45minutes). You can try to trick the thermostat or other such manuevers but I have found a setup that works well for me. I have not tried to trick the thermostat as the oven is not well insulated and the surrounding cabinets get hot even at 500F. What has worked well for me is to place a stone on the floor of the oven and another stone about 3 inches below the broiler. The stone on the floor will get very hot, it peaks at about 650F then cools as the rest of the oven warms and the thermostat kicks off. It will however tend to fluctuate between between 550-600F after reaching its peak as the burner cycles on and off. You can use an infrared thermometer to follow it and launch your pie at your desired temp. After the pie is on for about a minute I turn on the broiler. At about 2-3 minutes I transfer the pie to the broiler stone and rotate it to brown evenly, at the very end the oven door is open as I sort of "dome" it on the broiler to get some good char if not already there. The whole process takes about 4 minutes. I have found the stone under the broiler only gets to about 475F or so and the extra 100F-150F of the stone on the floor makes a big difference.
