I need split tabbed document MDI vertically and horizontally

I need to be able to split tabbed MDI documents vertically and horizontally.

Currently once I select one of directions (vertical or horizontal) to split tabbed MDI documents, I cannot select another direction to split other tabbed documents, I have to use the same direction all the time afterwared.
For example if I have three tabbed documents I cannot rearrange my documents as the following layout

------------------------------------------
|
Doc1 | doc 2
|
-------------------------------------------

Doc3

-------------------------------------------
I am really looking for having this feature in the coming release patch.

It seems that UIStudio only allow having the following layouts for given three tabbed MDI documents.

Either all horizontally

Doc1 | doc2 | doc3

Or all vertically

Doc1
-----
Doc2
-----
Doc3


Thanks!