How to prevent XamlWriter.Save from serializing the BaseUri property?

I'm making a theme editor for a WPF application. I generate XAML files dynamically, then I compile them into a DLL that is used by the application. The code used to generate the XAML files goes along those lines:

var dictionary = new ResourceDictionary();
...

dictionary.Add(key, new BitmapImage { UriSource = new Uri(relativePath, UriKind.Relative) });
...

XamlWriter.Save(dictionary, "myDictionary.xaml");

My problem is that XamlWriter.Save also serializes the BaseUri property:

<BitmapImage BaseUri="{x:Null}" UriSource="Images\myImage.png" x:Key="myImage" />

The result is that when the application tries to fetch this image, it doesn't find it because BaseUri is not set. Normally the XAML parser sets this property (through the IUriContext interface), but when it is already set explicitly in XAML, the parser doesn't set it, so it remains null.

Is there a way to prevent the XamlWriter from serializing the BaseUri property?

If I was serializing a custom class, I could add a ShouldSerializeBaseUri() method, or implement IUriContext explicitly (I tried both options and they give the desired result), but how to do it for BitmapImage?

As a last resort, I could load the XAML file and remove the attribute with Linq to XML, but I was hoping for a cleaner solution.

I eventually solved the problem by generating the XAML manually with Linq to XML.