Encoding H.264 while preserving RGB colorspace / 4:4:4

[nnezz]

I have pure RGB video, mostly CGI type footage, that I wish to encode in H.264 while preserving the full 4:4:4 chroma.
From what I can read, the specification supports it via the H.264/AVC High 4:4:4 Intra/Predictive profiles.
But, I can't find any information on how to use this or which applications/encoders support it.

x264 won't take anything but yv12, so where do I go to encode in the full RGB colorspace?
I realize that RGB encoding currently is (much) less efficient than YV12, but I can live with that, as long as I'm able to do it

Please, any help on the subject is greatly appreciated.

Reference: High-Fidelity RGB Video Coding Using Adaptive Inter-Plane Weighted Prediction

(if I confused any terms, excuse me. I'm still learning)