Another option is to use pnputil.exe to inject the NIC drivers into the base image's Windows PnP store so that the drivers will be there when PnP runs during sysprep.
Syntax is: pnputil.exe -a c:\drivers\nic\e1c62x64.inf
I've experienced the same thing you have many times. When a new model comes out with a new nic, I inject the new driver into the PnP store.