Is there a way to add your own controls to Blend's "Group Into" and "Change Layout Type" options?

Question

In Expression Blend 4, we can right click on an object in the Objects and Timeline panel to access the handy functions "Group Into" and "Change Layout Type":

However, what I really want often times is to be able to "group into" or "change layout type to" some of my own WPF content controls, such as a SunkenBorder, ClippingBorder, TransitionContentControl, etc. Is there a way that we can tell Blend to also include some of our controls (or any non-standard WPF controls) in these lists?

Update:

After I originally asked this question I had the idea to take a look at the source code of some of the panels that Expression Blend does include in its lists (Grid, StackPanel, etc), in the attempt to find a class metadata attribute that Blend might be paying attention to in order to populate these lists. I was hoping to find some attribute analogous to the ones you can specify for your own attached properties that allow them to show up in Blend or Visual Studio in their property panels. Unfortunately I did not find any such class attribute, so it appears that Sorskoot is correct, that we cannot add to these lists that Blend shows.

Answer 1

As far as I know these values are hardcoded and visible depending on the platform you are developing for.

Only Grid, StackPanel, DockPanel, Canvas, ScrollViewer, Border, WrapPanel, UniformGrid and Viewbox are available in Expression Blend 4. In Expression Blend for Visual Studio 2012 the list is somewhat extended but still hardcoded.

Too bad. I agree it would be a great to be able to customize this feature.