New Post: How can I add attributes to a Dir?

I've run into a scenario where I need to add some custom attributes to some of my Dir objects. I looked over the Custom Attributes sample, and I've come up with this code:

Dir someDir = new Dir(@"path\to\dir", new Files(@"path\to\files"));

someDir.Attributes = new Attributes() { { "DiskId", "2"} };
//or
someDir.AttributesDefinition = "DiskId=2";

The trouble is when I run Complier.BuildWxs(), the attributes I add are not reflected in the generated .wxs file. Due to some debugging, I know the attribute does exist in my Project object, but I'm a little unclear as to why it isn't shown in the wxs after compilation. How can I add these attributes so they show up properly?