How to vertical text overflow in LibreOffice Calc?

I have a spreadsheet, the row height is fixed to 7 mm but in some cells I need to put big text - it has almost double the height of the cell. The cells above are empty so I need the text to overflow vertically too, and to overwrite on those cells above.

Is it possible to do this?

I am using LibreOffice, on Windows 8.1 (had no time to upgrade these days)

As the cell above is empty, you could merge both cells.