If your kernel requires you to run node_exporter as root, and you have no way of configuring policy to allow access to /proc and /sys, then I guess you don't really have any option.
I use exporter_exporter in front for TLS termination and certificate authentication, and it works fine. I believe node_exporter 1.3.x can do its own TLS and auth via --web.config, but exposing a root-running process directly doesn't sound like a great idea.