Well first off Steve, don't ask for a "cooker" resistor, I just used that as slang, as a wirewound resistor is one that usually gets hot. That's why they have ceramic bodies and are filled with actual sand or synthetic materials so they don't catch on fire.
Now, what you can do (this won't be pretty or 1000 point show car correct) is go to radio shack and buy (2) of the 8 ohm 20 watt non-inductive resistors and wire them in parallel. This will yield 4 ohms. And since they're 20 watt, they'll more than handle the heat--probably never have to replace again in your lifetime. Since you have (2) switches, you'll need (4) of these 8 ohm resistors.
These are quite big though, so mounting will be a challenge, an actual 4 ohm 5 watt unit from an electronics supplier will fit the little mounting assembly apart of the switch (it's a metal clamp).
I will check my factory assembly manual for the mysterious ground location for the motor itself. Will let you know.