Items needed and whether it will work, to put a switch in a car that will turn power to a blue tooth transmitter?
Pull the panel and put a toggle switch on the power wire to the lighter. Car audio shops or car accessory shops can help you with the parts.
You would have to install the switch on the wiring going to the lighter receptacle, That would requiring removing the receptacle or getting behind the panel. The switch would have to be rated to handle the amperage of the cigarette lighter (check the fuse value). While household wire nuts would work for connecting the wires once you cut them, soldering and shrink wrap would be safer and more professional. If you have no soldering skills, then crimp connectors and a crimp tool would work. And, of course, you'd have to figure out how and where to mount the switch. Any good hardware store or auto parts shop should have what you need. Since you had to ask, I'm guessing this would be a very challenging project for you do..
Get a standard 3 foot accessory socket extension, they usually have 16 gauge electrical zip cord. Then get one of the inline spice spin dial light cord switches from home depot to install in the cord. Option 2 is to add a SPST rocker switch on the accessory socket feed wire. Option 3 is to wire up an external cord socket on a key switched fuse box power lug. I would go with option 3, and then you can run the cord into the glove box out of the way. This is how I usually add a bluetooth FM modulator adapter so the entire unit is protected. The only downfall is if your adapter has an IR remote and must have line of sight access.