You don't need dc power to heated grips. They are just resistor elements and work both ac and dc power. If your set has some kind of "sophisticated electronics" and is marked as "DC only" I would leave it to shop. The simplest is the best.
My EC 300 is equipped with heated grips. They are very useful (must have!) in Finland's cold winter climate.
My assebly is as minimal as it can be. Power wire and fuse -> on/off switch-> wires to heater elements-> wires from elements to ground (=frame). Wrap up glued (they usually have sticking surface inside) heater elements with electric tape and use grip glue to grips.
If you have separate resistor in your set you can use it to balance temperature in between right and left grip. Right gets hotter if you have plastic throttle control.