Short answers:
1) Not I.
2) I accomplished the same thing with the Skene products.
On my two Burgman 650s, I accomplished what I think you're trying to do by replacing the old-school turn-signal single-filament sockets and bulbs with duallies. See this pic/caption and the next couple in my Burgman gallery:
Closer to current times, LEDs, etc., on my Victory Cross Country Tour, I attempted to do a similar trick with a product designed to do that from Custom Dynamics (where I also got a brake flasher for the Vic, and a license-plate-frame flasher many years before that). Alas, I never could get this to work -- the CANbus was too much of a nanny -- and abandoned ship.
Custom Dynamics has a module that
might work:
Our SMART Triple Play® module converts rear 1156/7507 turn signals (models with a center taillight) to function as run, brake, and turn with choice of 10 user selectable built in brake light strobe/flash patterns (user can also select no strobe/flash on brake). Additional functions include...
www.customdynamics.com
I have no experience with that. When I bought a product from them for the Victory, it was a much simpler in-line device -- something like $25 for a pair of them (I can't find the product now) -- but this device looks like it
might accomplish what you want. I would imagine that no one has ever tried this on a C 400, though. So you could be the guinea pig, much as I believe that I was for the Skene products on our scooters.
Some folks have asserted over the years, by the way, that even if one were to get this to work you would then need to be concerned about the heat buildup inside the confined areas, given that an LED would be on all the time. I'm just reporting this, i.e., I'm not necessarily a believer. As I say, I tried and failed, with my Victory (which had LED turn signals), with its front turn signals.
Now, if you'll review my Skene Photon Boosters (not Blasters, but Boosters) up-front installation, I have full-time amber running lights that are akin to having the turn signals lit all the time. And while the don't blink -- that's left to the stock turn signals, the Boosters are much brighter than the turn signals.
In the rear, the Skene P3-TS do both functions, and very brightly. They're in addition to the stock signals doing their stock thing.
So, if I understand your question correctly, you have a nice clean idea, but I don't know how to accomplish it without throwing extra lights at the problem, with the possible exception of that $100 Triple Play device (or something similar).
Good luck.