The closest thing i could find was using the activities.list home=true with type "upload" i found it via https://code.google.com/p/gdata-issues/issues/detail?id=3946
But it doesn't seem to be the same as the subscription feed (tested here https://developers.google.com/apis-explorer/#p/youtube/v3/youtube.activities.list ) .
I don't know how you made your api, but this guy made this https://github.com/DouglasMeyer/YoutubeNewSubscriptionVideos (a guy made it on the issues link, scroll waaaay down), maybe it's implementable for OV.
Also, do you use activities.list for grabbing videos or playlist.list? it seems activities.list does resembles the way you used on apiv2 when choosing a user