How do I make a WrapPanel with some items having a Height of *?

A deceptively simple question that I have been trying to solve. I want a control (or some XAML layout magickry) that behaves similar to a Grid that has some rows with a Height of *, but supports wrapping of columns. Hell; call it a WrapGrid. :)

Here's a mockup to visualize this. Imagine a grid defined as such:

<Window xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
        xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
        Title="Window1" Height="400">
    <Grid>
        <Grid.ColumnDefinitions>
            <ColumnDefinition Width="*"/>
        </Grid.ColumnDefinitions>
        <Grid.RowDefinitions>
            <RowDefinition Height="Auto"/>
            <RowDefinition Height="*"/>
            <RowDefinition Height="Auto"/>
            <RowDefinition Height="*"/>
            <RowDefinition Height="Auto"/>
            <RowDefinition Height="Auto"/>
        </Grid.RowDefinitions>
        <Button Grid.Row="0" MinHeight="30">I'm auto-sized.</Button>
        <Button Grid.Row="1" MinHeight="90">I'm star-sized.</Button>
        <Button Grid.Row="2" MinHeight="30">I'm auto-sized.</Button>
        <Button Grid.Row="3" MinHeight="90">I'm star-sized, too!</Button>
        <Button Grid.Row="4" MinHeight="30">I'm auto-sized.</Button>
        <Button Grid.Row="5" MinHeight="30">I'm auto-sized.</Button>
    </Grid>
</Window>

What I want this panel to do is wrap an item into an additional column when the item can not get any smaller than its minHeight. Here is a horrible MSPaint of some mockups I made detailing this process.

Recall from the XAML that the auto-sized buttons have minHeights of 30, and the star-sized buttons have minHeights of 90.

This mockup is just two grids side by side and I manually moved buttons around in the designer. Conceivably, this could be done programmatically and serve as a sort of convoluted solution to this.

How can this be done? I will accept any solution whether it's through xaml or has some code-behind (though I would prefer pure XAML if possible since xaml code behind is tougher to implement in IronPython).

Updated with a bounty