I've written earlier about my installation of Hella DRLs here. For those of you who don't want to add anything to the front of our car, there's another solution:
DRL-1 Daytime Running Lamp Module Installation
This module illuminates both turn signal lamps steadily except when they are flashing as turn signals. I spoke with the seller about this product, and he states that the module should be transparent to all varieties of body control modules, but he does not recall any orders specifically from X351 owners. He's an honest and knowledgeable vendor/consultant with whom I've purchased several products. If you have an earlier X351 without DRLs, I urge you to consider adding some. Your car is invisible to those SUV morons out there.

 

To anybody looking to do this upgrade, I would recommend that if you are using the "quick splice" connectors, that you use them inside the body/passenger compartment of the car. While they make for easy connections, give the car a few years (especially in a salt use area) and those quick connections are going to be a heart ache with random issues. If you need ideas, let me know. I have to make connections that will survive a nuclear meltdown (literally). I know a few tricks.