Populate Uocdropdownlist dynamically

Hello experts,

I have a requirement to build a custom RCDC UI.

It should contain two dropdownlists 

1. Regions

2. Organizations

We have fixed number of regions for which I have used XMLDatasource.

<my:XmlDataSource my:Name="regions"><Regions><CountryRegion Code="" Name="" /><CountryRegion Code="Reg1" Name="Region1" /><CountryRegion Code="Reg2" Name="Region2" /></Regions></my:XmlDataSource>

But We need to populate the organizations based on the selected region.

I have tried using one more xml reference as shown below:

<my:XmlDataSource my:Name="Organizations"><Organizations><Reg1><Organization Code="" Name="" /><Organization Code="Org1" Name="Org1" /><Organization Code="Org2" Name="Org2" /></Reg1><Reg2><Organization Code="" Name="" /><Organization Code="Org3" Name="Org3" /><Organization Code="Org4" Name="Org4" /></Reg2></Organizations></my:XmlDataSource>

And my UocDropdownList controls are shown below:

<my:Control my:Name="Region" my:TypeName="UocDropDownList" my:Caption="Region" my:Description="" my:RightsLevel="{Binding Source=rights, Path=Region}" ><my:Properties><my:Property my:Name="Required" my:Value="false" /><my:Property my:Name="ValuePath" my:Value="@Code" /><my:Property my:Name="CaptionPath" my:Value="@Name" /><my:Property my:Name="HintPath" my:Value="@Name" /><my:Property my:Name="ItemSource" my:Value="{Binding Source=regions, Path=/Regions/*}" /><my:Property my:Name="SelectedValue" my:Value="{Binding Source=object, Path=Region, Mode=TwoWay}" /></my:Properties></my:Control><my:Control my:Name="Organization" my:TypeName="UocDropDownList" my:Caption="Organization" my:Description="" my:RightsLevel="{Binding Source=rights, Path=Organization}" ><my:Properties><my:Property my:Name="Required" my:Value="false" /><my:Property my:Name="ValuePath" my:Value="@Code" /><my:Property my:Name="CaptionPath" my:Value="@Name" /><my:Property my:Name="HintPath" my:Value="@Name" /><my:Property my:Name="ItemSource" my:Value="{Binding Source=Organizations, Path=/Organizations/%Attribute_Region%/*}" /><my:Property my:Name="SelectedValue" my:Value="{Binding Source=object, Path=Organization, Mode=TwoWay}" /></my:Properties></my:Control>

Unfortunately, this approach din't work for me as %Attribute_Region% is not available for the object as this RCDC is used for creation.

Is there any better approach for achieving this?

Please advice.

Thanks and Regards, Siva Kumar Balaguru