You can't right now. You can get 4k capture cards and HDCP strippers and capture to hard drive. But that's all. You can't take that video and burn a UHD bd yet - PC players don't yet exist, never mind software to author a UHD bd. Or drives capable of playback.
Well you can burn a bdxl disc with those files to avoid filling your hard drive
Is there any indication when UHD-R and PC drives will be shipping? This seems a lot slower release schedule than Blu ray/HD DVD as there were recordable discs at launch. I haven't found any info at all.