I guess I should start off this post by saying what I'm doing is a dirty hack, in no way supported, and in general a terrible idea. But it's also really awesome.

I'm not going to cover how to setup your unattend file, or how to customize a PE image… there are plenty of people out there who have covered those topics. What I do want to cover here is how to edit your PE image so that you can force it to connect to a specific WDS server. This will help solve the problem where you want to deploy computers into two domains on the same subnet, but WDS only looks for prestaged computers objects on the domain it is joined to.