How to conditionally deploy an app.config based on build configuration?

Question

I have three custom build configurations { Dev, Qs, Prd }. So, I have three app configs { Dev.config, Qs.config, Prd.config }. I know how to edit the .csproj file to output

Answer 1

How about using a build server?
Its been a long time since I've worked in .NET but can't you use Hudson(-like) server for managing your build configurations? Isn't it easier?
And what about NAnt? Doesn't it suit your needs?