You'll need to tap into your wiring harness and wire in a "trailer light converter" along with a brake controller into a seperate plugin. Other option is to add a couple temporary blinkers to your gooseneck. Electric brake controllers work off of the brake light switch so you will be fine there. The problem you run into is almost all goosenecks are wired so that the brake lights and the blinkers run off of the same wire as do most domestic vehicles. Semis are setup so that the brake lights and the blinkers are on seperate wires and seperate lights.

$90 for a Tekonsha brake controller and $12 for a Peterson light converter and a couple hours in the shop would have you going.