Hi Arthur,
Visual Studio requires that design-time assemblies be located in a subfolder called "Design", which is in the same folder as the control's assembly. If you look at the Assemblies folder after installing WPF Studio, you will see that we add the Design folder with the appropriate files. If you copy the assemblies to a network drive, you'd also need to copy the Design folder.
This should work, but if it doesn't then it's really a Visual Studio issue (since it's the one looking for and loading the design-time assemblies).