Bound DataGridView newrow combo box

Hi,

What I want to do, and am not sure how to do is the following:  I have a datagridview that is bound to a List data source. I made the rows loaded  from the data source as "ReadOnly" because I don't want the user to be able to edit them, but I want to allow the user to add new rows to the data grid view (which I am doing with "AllowNew") and  I want the user to be limited to a list of options for a specific column.  In other words I want to add a combo box to column in just the "new" row.

How do I do that?

Thanks in advance.