Inserting new rows and moving existing ones with OpenXML SDK 2.0

I'm using OpenXML SDK 2.0 to add data to the spreadsheet template but I ran into a problem (since I've been using OpenXML for a day that's not so hard to believe). I can't figure out how to add new rows while pushing all the rows that are below the new ones down.

Here is the spreadsheet template I'm using. To be more precise, what I want to achieve is to move those slate colored rows to the bottom while adding data to the white colored rows.

The code I'm currently using is identical to the one on MSDN - Creating Documents by Using the Open XML Format SDK 2.0 (Part 2 of 3)

I believe that the catch is somewhere in this part of the code:

                    sheetData.AppendChild(polaznikRow); 

I've also tried experimenting with InsertAfter, InsertAt ,etc. but without any success.

Any help would be appreciated.