Add extra VPN interface in custom build

Is it possible to have an extra interface added like a L2TP VPN connection?

I would like to have my build autoconnect to a default VPN account so i can configure it from the VPN server incase the device needs to goto factory defaults or something like firstboot.

So far i found the file below that looks like it creates the entire network. (Please correct me if i'm wrong)

openwrt/package/base-files/files/bin/config_generate

Is it possible and if it is could someone point out an example on how to let it create the extra interface during setup?

Thanks in advance