As the poster above pointed out in the link, you can just short your LP lights to share the load of the bulb to one of the rear lights. You don't really need to short both both the the left / right rear lights to the trunk light.... Just remember that it's the positive leads you want to short together... (don't short the positive to ground...)
Doing it this way is actually much better since it tricks the computer to seeing the load of a bulb without creating unecessary heat. A paralleled resistor would just dissipate the energy in the form of heat...
Downside to this method would that if the tail light bulb that you connected to goes out, you'll get two warnings, one for the tail light, and one for the License Plate light.