You can have any event triger the "Add Item" action but something has to trigger it. Rememeber what you are doing is adding another page to a pagelist on the server so you will need to force a postback to save the values you entered in the row back to the clipboard on the server. You cannot insert something into a section, a section displays properties from the clipboard. If you describe what you are trying to do rather than how you think you should do it perhaps I can assist you further.
The way the grid layout works is that it is generated on the server by looping through pages in a pagelist property or datapage or a report and creating a row for each page. The way rows get added to the grid is by adding a page to the pagelist and regenerating the grid. What is your grid bound to? What would trigger adding a new row? If you don't want to show data from clipboard or have user put data in the row to be put on clipboard then what do you want a row for? In the context of a reapeating grid what you are asking does not make much sense.
If you describe the business use case you are trying to accomplish, ie describe the functionality from a business user point of view, perhaps someone may be able to help you.