At only 55 watts you could use a very small power inverter like
this. Gives you a few USB charging ports too ;-)
Sadly though without cracking it open and feeding 12v into the regulator boards inside, its a no-go for DIRECT 12v power.
EDIT: The small inverter I have like that has a power switch on it, which is nice for off grid, since you can stop any parasitic power drain with the inverter switch then, TV direct to 12v means you have to unplug it to eliminate the parasitic drain. NOTE the inverter I linked doesnt have a switch, so I would shop around.
