I am personally abusing the block feature for this. I haven't tested if it is actually true, but I began blocking channels that I am not interested in and haven't noticed anything being recommended yet from any channel I remember blocking.
Kudos, gonna try!
It's lame that it has to be done that way, but it's the best way I've been able to do it.
How else do you think they can figure out what you hate vs you don't like but don't hate either ?