How do I mark a video as watched with Youtube API v3?

I have a C# program I wrote using the Youtube API V3 that manages my channel's videos.I already have all the OAuth 2.0 stuff sorted out and I'm looking for a way to tell Youtube that the authenticated account watched the video.The reason being that I use the "watched" feature to determine which of the videos in my feed is the last one I actually watched.

Is there a way to do that?Or is it purposefully not in the API because it messes with the view count?

Of course I checked Google and Google's API reference first, didn't find anything.