N314:
What is the simplest/easiest way to bump 5 volts to 12 volts?
You need to use a separate 12 volt supply. Tie the Arduino ground to the 12 ground and the transmitter ground then tie the +12V to the transmitter. If you're trying for battery operation you can use a 12volt battery with enough milliamp hours and use it to power the arduino and transmitter.