So back to trying to work around this. I gather NetBSD uses ifconfig.interfacename files like OpenBSD uses hostname.interfacename files. The hostname.em0 for my ethernet card looks like: inet 192.168.0.7 255.255.255.0
The device on a Pi is usmsc0, so you just need to create ifconfig.usmsc0, mygate, mygate6 (if applicable) and resolv.conf.
John