Could you mount X10 motion sensors and have them control wall switch modules?
The Eagleeye type of motion sensor is very small and versatile. That could trigger lamp modules, appliance modules or wall switches that would turn on lights, appliances, etc. It could trigger on motion, motion only at night, or simply turn something on at dusk and off at dawn.
In your scenario, having a small eagleeye sensor outside could trigger a wall switch module to turn on your carriage lights. It would require the MS-14 motion sensor, a TM-751 or equivalent, and a wall switch module - I like the XPS-3 so you can use fluorescent bulbs.