Different power sources - Same function.

We all pretty much know how we can tap into ant 12Volt power source and use it as the power to our lights.
This is what Im trying to figure out: Can I tap my windshield wiper nozzle lights into my turn signals so they will blink with them but also have a main On / Off switch as well that I can use if I see a cop and don't want the bright green to attract his attention? Female cop? Well I acctually do try to have them pull me over. But thats a whole different topic.
Is this idea feasable? Would I need relays? If so, how and where?

I just have one thing to say: PLEASE get rid of your windshield wiper nozzles. They look like crap IMHO.

A transister with a diode would probably be your best bet. The transister would allow you to switch your lights on and off with the blinker each time the blinker clicked on and off without having to wait for a relay to click over each time. In addition, the one way diode would allow you to send power to your LED's to turn them on when you want, without sending power back down the line to your blinkers. (You'd put the diode in line between the transister and the LED so that power wouldn't kick back the wrong way into the transister and cause damage to it, or the blinkers).

Good point Steven! =P

Alright. You kinda lost me with that but I'm sure it can be done somehow. Any one got a diagram?