These instructions will allow you to encode yuv420p10le with ffmpeg while using nvenc. Note that other pixel formats have not been tested and may be broken. I do not suggest using this as your main ffmpeg installation. You also need to install the nv-codec-headers and other dependencies as required by ./configure when building.
git clone https://github.com/FFmpeg/FFmpeg
cd FFmpeg
git apply nvenc-yuv420p10le.patch
./configure pkg_config='pkg-config --static' --prefix=/usr/local --extra-version=ntd_20150126 --disable-shared --enable-static --enable-gpl --enable-pthreads --enable-nonfree --enable-fontconfig --enable-libfreetype --enable-libass --enable-libfdk-aac --enable-libmp3lame --enable-libopus --enable-libtheora --enable-libvorbis --enable-libvpx --enable-libx264 --enable-filters --enable-runtime-cpudetect
make -j8
# Do not run sudo make install, just use the ffmpeg as-is.