I just swapped my brakes to Shimano Saints and used the barb and it
worked great. It is a little bit of a pain in the butt to screw it on, but it works.
I also made sure as I was pushing one side I pulled on the other side so that
there was minimal stress on where the barb Is connected.
No you can do it with motor in. Feed from rear. You do need to take the belly plate off and it's easier if you drop the forks. Underneath it you can take the fed hose When look up the inside of the downtube you'll see a carbon sleeve, but of a faff but feed it up the middle. It'll pop out on the left hand side of the headtube just feed it through.