That's what I ended up doing. Still can't seem to beat him though...
Such a great game.
i've not got to him yet, and i'm starting to feel a bit stuck, as the only place I can go (that i know off) is the nightmare off (????) (the nightmare accessed from the library that isn't the nightmare frontier). And it's not that the place is hard, it's just Frenzy is such utter bullshit I can't be bothered with it. I also feel like I'm ripping through the game too quickly, at 20 hours currently, and have done a LOT of co-op during those 20 hours.
Somewhere in the forbidden woods is the deep sea caryll rune that grants a huge boost to frenzy resistance. You still need to be careful around those frenzy-singing bitches, but if you are quick you can take them out before the frenzy recks you, or at the very least you won't have to suck down sedatives every other second to survive.
There are also a bunch of places off the beaten path that can be hard to find if you'd rather, like the upper cathedral and Cainhurst.