You are dropping minimum of 6-9V. The LDO only needs a third of a volt of overhead at this level of current.
A linear regulator is essentially a variable resistor with feedback. And in this circuit, the minimum value of that variable resistance is exactly 50R = (11V-5V)/0.120A. You could put up to a 45 ohm series resistor rated for 2/3W between the power rail of the car and Vin on your LDO, and still get a minimum Vin of over 5.5V at 120mA max draw. When you do this, the regulator has to drop only a small fraction of the total, when at max draw of 120mA. That is if you are using 11V as the minimum voltage of the vehicle when the engine is off; personally, I would go 10.5V. To allow copious room for error and tolerances, I might try 40R 1W resistor.
This will dissipate up to 2/3 of that 1W of heat in the series resistor when the engine is running (and even larger percentage of the total wattage when the engine is off), which you could strategically place away from your regulator. A resistor can typically run up to 200C, sustained/indefinitely, which means it can operate at a higher differential to ambient which means you can effectively get that level of dissipation with less copper/heatsinking. With a thru hole part, you can achieve this largely through ambient air cooling, with relatively smaller amount of heat back dissipated by the PCB other than what is transferred through radiation and through conduction via the resistor leads. In addition, a resistor has a positive temp coefficient to prevent runaway failure, and it can be strategically placed anywhere you want on the PCB to keep it away from the regulator and other high temperature and/or temp-sensitive silicon.
The series resistor might induce oscillation/instability of the Vout, particularly because this is a LOW DO regulator. But it depends on your load and power supply and is not necessarily going to be a problem; if it is a problem, more low ESR input caps in parallel might be all it takes. A voltage regulator is designed to give a stable Vout despite change to Vin and/or load. Using it as a power resistor is fine when you have excess capacity. If you are cutting it close, might as well separate the two functions and leave the regulator to only disspate closer to the minimal amount of heat that it must to take care of the variable part of the equation.
Depending on how you want to look at it, you could also view this series resistor as increasing the output impedance (voltage sag under load) of your Vin rail in such a way that at max load the rail barely covers the overhead requirement of the voltage regulator.