You may not be able to do this. I am not sure, I will have to really study the prints.
For one thing once power for the heating system leaves the fuse panel, it runs to a relay and then back to a heater control module.
The grip heaters have build into them a certain ohm (resistance) depending on what setting you put them on, the power flow does come from the heater control unit and back to it and depending on the resistance sensed by the themistors, allows voltage in various amounts to flow and cause the grip heaters to work. All this whole business is also tied to the ECU unit and if an open short or excess current draw is sensed it shuts the whole business down.
To just jump the wires at the seat pin connector? Hum......do not think so as then you lose the resistance sense and do not think the heater control module will function with out the proper sense of resistance.
If it were my bike I would do one of three things.
1. Forget them and install aftermarket heated grips, come direct off the battery with a separate relay and off on switch and thermostat.
2. Utilize the existing grips, but also run direct off a separate relay and find some type of thermostat that is controlled by resistance to control the heat, and install that. Resistance through any substance with heat and current changes as the heat increases, and that is how that kind of thermostat works.
3. Install the element out of the stock seat into the new seat. The seat company people many times do this. In fact some build a seat with heating capacity to it. But also some simpy use your existing saddle and incoporate the heating elements into the new seat.
4. There is the possiblilty that you could run the wiring for the grips direct to the front seat heater thermistor, and then back to the relay, through the heater contol unit. I am not sure about this, would have to have the bike with the seat off, tupper ware and left saddle back off, and it would take extenive trouble shooting with a meter to actually know if it would work.
Okay Ready to blow a fuse? It is fuse number 11 just so you will know.
I have studied the schematic and it is on page 26-35 of the service manual. It shows that the grip heaters and the seat heaters is rigged in series. Therefore with an open circuit no power will flow to the grip heaters.
However the grip heaters are controlled by the seat thermistors. And power has to flow through the heat control unit to work.
So I think, I am not sure, but I think, that a simple jumper across the wires at the seat pin connector across the yellow/red and red/white wire will allow the grip heaters to work.
English Bob has tried the technique of jumping the two wires across the pin connector at the seat. It does not work. The grips work fine connected, but do not work with the jumper installed.
One then has to assume that the heat control unit is designed to sense the resistance of the heating elements and without those in place, the diodes in the heat control unit will not allow current flow. Trying to install a resistor to compensate for the resistance of the heat element would not work well either as the resistance would change with the ambient temperature.
In essence with out a heating element in series in the circuit the grips are not going to work without it. As designed.
Naturally one can redo things and use a separate thermostat, re wire and so on. But the stock system is not going to function with the heating element out of the system.