Vista - Dynamically Loading XAML ResourceDictionary which includes otherXAML files

I'm dynamically loading a ResourceDictionary ( via
Markup::XamlReader::Load ) in my application. It works fine unless the
XAML file references another ResourceDictionary to load like this -

<ResourceDictionary.MergedDictionaries>
<ResourceDictionary Source="Shared.xaml" />
</ResourceDictionary.MergedDictionaries>

The Xaml Reader fails with the following error

Additional information: 'Shared.xaml' value cannot be assigned to
property 'Source' of object 'System.Windows.ResourceDictionary'. Cannot
locate resource 'shared.xaml'. Error at object
'System.Windows.ResourceDictionary', Line 6 Position 25.

The included Xaml file is in the same path as both the executable
loading as well as the main .Xaml file. The path to Shared.Xaml is also
in my environment path.

Is there a way to give the XamlReader a path to search for referenced
files? It works if I use the full path to Shared.xaml in the Source
attribute but that's not a workable solution - I don't want to have to
edit a bunch of .xaml files when my application install directory changes.

Thanks-

John Dunn
QSC Audio Products, Inc.