I looked at this, and had the impression you can contact support at DO and they'll mount a rescue mode image where you could setup btrfs manually. The idea of

I looked at this, and had the impression you can contact support at DO and they'll mount a rescue mode image where you could setup btrfs manually. The idea of having to depend on support to just boot an arbitrary image didn't really appeal to me though, so I wound up just using Linode and creating the root filesystems from their Finnix image, which worked fine.