Default MIME type for files in Visual Studio 2010

Does anyone know how to set the default MIME type in Visual Studio 2010. When I create a new Silverlight page the .XAML file gets a MIME type of application/unknown and I'd like it to be set to text/plain.

The MIME type can be changed via Right Click > Properties > File Properties > MIME Type but I don't want to have to change each file when it is 开发者_开发知识库created.

Any help very much appreciated,

James