Generic, bindable, uniform-stretch layout - wpf

Question

Excuse the length, trying to ensure all info's contained!
I need a view of cells (a view with corresponding VM) almost in a circle like so:
********
**********
************
**************
**************
**************
**************
************
**********
********
A few of the complications:
Before we fire up I don't know how many cells to display. All cells must be equal in size. The entire view must be scalable.
In my simplified world, my window creates 20 RowViewModel objects and passes each constructor the number of columns it should create.
My main view:
<Viewbox Stretch="Uniform">
<ItemsControl ItemsSource="{Binding RelativeSource={RelativeSource Mode=FindAncestor,AncestorType={x:Type Window}},Path=Rows}" >
<ItemsControl.ItemsPanel>
<ItemsPanelTemplate>
<UniformGrid Rows="{Binding Path=Rows.Count}" />
</ItemsPanelTemplate>
</ItemsControl.ItemsPanel>
</ItemsControl>
</Viewbox>
And my RowView:
<Grid>
<ItemsControl ItemsSource="{Binding Columns}" >
<ItemsControl.ItemsPanel>
<ItemsPanelTemplate>
<UniformGrid Columns="{Binding Columns.Count}"/>
</ItemsPanelTemplate>
</ItemsControl.ItemsPanel>
</ItemsControl>
</Grid>
My cell view:
<Border >
<Viewbox Stretch="Uniform" >
<Label FontSize="10" Content="{Binding Notice}" Foreground="White" />
</Viewbox>
</Border>
As it stands, all rows are the same width so rows with fewer cells have wider cells. If I tell each row there are 20 cells, each cell is the same size but everything aligns left despite HorizontalAlignment settings, presumably because it appends blank cells. I'm assuming I could insert blank cells where I want them but this feels like a fudge of the data to make the display right, which I'm sure you'll agree is B-A-D.
I've tried squillions of approaches and think this is the closest so far but I'm missing it. Can you help please?
Thanks for your patience.

Answer 1

Well, maybe it's impossible? I ended up adding a property to the ViewModel that builds the grid and assigns the appropriate row/column during the generation, then databinding a contentcontrol to that grid.
It remains unsolved - how to do it in XAML?
The view:
<Viewbox Stretch="Uniform">
<ContentControl Content="{Binding PrettyGrid}" />
</Viewbox>
In the ViewModel:
public Grid PrettyGrid
{
get
{
return BuildGrid(data);
}
}
and the BuildGrid snippets:
private static Grid BuildGrid(List<objects> cellData)
{
var localGrid = new Grid();
// ...
localGrid.RowDefintions.Add(...);
localGrid.ColumnDefinitions.Add(...);
cellData.ForEach(cell =>
{
ContentControl ctl = new ContentControl();
ctl.Content = cell;
Grid.SetRow(ctl, cell.Row);
Grid.SetColumn(ctl, cell.Column);
localGrid.Children.Add(ctl);
});
return localGrid;
}