Jeff Wilcox has a guide and a video on how to build Silverlight code on machines without the SDK.
Part of the Silverlight SDK can be copied into your source tree to build projects on machines without requiring Silverlight or the SDK. This is great for continuous integration environments and build labs where having an independent build is key. I’ve compiled a quick screencast (6:07) that demonstrates preparing a directory to check in the proper SDK components, updating a C# project file, and then proving the result by uninstalling the Silverlight SDK.