FlexLayout mix of resizing

[valimaties]

Hi.
The FlexLayout has the dependency property Direction, an enum which has 4 values: Column, ColumnReverse, Row and RowReverse.
I need that this FlexLayout to be able to populate by Column but not to resize itself to the Right (Horizontally) but Vertically.
What means that (explanation)?
I have a BindingList which contains 22 items (anything, this doesn't matter, only the number of them).
My FlexLayout is the child of a ScrollView, in the current window can display only 5 columns and 4 rows, which means that it can display only 20 of my BindingList items, the other two will be invisible to the right. Which means that when the number of items are not currently be able to display in the current view it will create invisible columns . I want that the FlexLayout to create invisible rows, not columns, which means that in this example the fifth item in the BindingList will be invisible and the sixth item will be the first item in the second column.
So, the approach will be to create invisible rows and only VerticalScrollBar of the parent ScrollView will be visible, not the HorizontalScrollBar.

V = visible item
I= invisible item

Now it populates like this, with HorizontalScrollBar

V1    V5    V9    V13    V17    I21
V2    V6    V10   V14    V18    I22
V3    V7    V11   V15    V19
V4    V8    V12   V16    V20

How I want to populate instead, with VerticalScrollBar visible only:

V1    V6    V11    V16    V21
V2    V7    V12    V17    V22
V3    V8    V13    V18
V4    V9    V14    V19
I5    I10   I15    I20

Let's say that this value of the Direction enum will be called ColumnVerticalGrow .

PS: The FlexLayout must be made also Virtualized, because it takes a lot of time to display a big collection of items.