Right, so, for the sake of anyone else wondering how to pull a Canyon Nerve apart, the short answer is: you're probably going to need a blind bearing puller (8mm collet and slide hammer worked for me).
You *might* be able to bodge it with an expanding 8mm rawlbolt, but I couldn't get that to work. If you try to force things with chisels and hammers round the back of the bearings, you're almost certainly going to trash stuff. At best you'll kill the fancy ball-joint washer that's hiding in there, which will be fun sourcing a replacement for. At worst you'll wreck the chainstay and/or main frame. So I'd really not recommend getting the Yorkshire spanners out on this job.
Once you've pulled one bearing a couple of mm out of its seat the whole assembly comes apart beautifully, no force required and there's really no way it can stay together if you've got one of the bearings even a little way out.
To be honest, having gone through all this it's clear I've wasted my time. If your Nerve's swing arm is still moving ok, I doubt you need to replace the main pivot bearings at all. They're not cartridge jobs with balls or rollers in them, they're spherical plain bearings, and they don't seem to wear in the same way as normal bearings. It's also pretty well sealed down there compared to the other bits of the linkage. If the bearings are not obviously completely dead I reckon there's no point going to the trouble of replacing them. I had to replace mine because I knackered one bearing in my attempts to pull things apart out of curiosity, but unless it's clear that you really need to do this job, don't bother...