Someone asked me the correct way to perform this mod. You will need this part:
http://www.customled.com/PRODUCTS/MA...ic_blinker.htm
One blinker for each bulb you want to use for both parking and signal.
Tap the parking and signal wires and route them to the blinker. Hook up the bulb you want to the blinker and ground as indicated in the instructions.
Now the bulb may be used for both parking and signal. The bulb will stay lit with parking, and will flash any time the signal is activated.
This is a much safer way than the way outlined in the first post.