a lot will depend on how your 'dummy' signals are currently set up. On my S200 the 'dummy' signals were not wired. The global indicator used in the rest of the world came with built in led bulbs in the housing so I sourced a pair of slightly used indicators from Ebay UK. You can then unhook and uninstall your US spec indicators and run the wires to your newly installed indicators.
If, however, your indicators are merely in need of a bulb, you can see if they are wired or if wiring is in there but not hooked up.
attaching a pic of the indicator I purchased, with already installed leds and wiring.