<ItemGroup>
    <MyCustomProjectType Include="..path_to_my_project">
        <Name>MyProjectName</Name>
    </MyCustomProjectType>
</ItemGroup>

<Target Name="MyTarget">
    <ItemGroup>
        <CustomProjectReferenceFiles
            KeepMetadata="Name"
            Include="@(MyCustomProjectType->'%(Identity)%(Name)***')"
            Exclude="***.x;***.y"
        />
    </ItemGroup>
    <Message Text="@(CustomProjectReferenceFiles)" />
</Target>