Sensing directional light
The custom shroud may be the easiest solution. There are a few variables that may change things depending on your application requirements such as, the light intensity, required sensor sensitivity, and resolution.

When directing light with LEDs, you can use a 'collimator' or a 'light pipe' both are available through digikey and other electronics suppliers.

collimator: http://www.digikey.com/product-search/en/optoelectronics/optics-leds-lamps-lenses/525154?k=collimator

light pipe: http://www.digikey.com/product-search/en/optoelectronics/optics-leds-light-pipes/524541

If you were doing a simple binary yes/no light is hitting here (maybe with a laser or focused high intensity light). I would use an LED and light pipe and used the LED as the photosensor. If you have incredibly low lighting, I would go with photoresistor and shroud. 

If you can find a clear light pipe that matches the footprint of your sensor, you'd have the perfect solution.