If I understand you correctly, what you can do is make a controller of your own which is defined in an additional form and then you can add it to your main form as much as you want. You can define this new controller (meaning a new form) to hold only a single line of the comboBox and then add it to a location in your main form which is based on the location of the previous controller.
Here is an example which adds several control of a class called CNewControl to a tab called newControlsTab one after the other.
int controlHeight = 0;
foreach (CNewControl newControl in newControlList)
{
this.newControlsTab.Controls.Add(newControl );
newControl.Dock = DockStyle.Top;
newControl.Location = new System.Drawing.Point(40, 3 + controlHeight);
controlHeight += newControl .Size.Height;
}
You can of course change it to add your line only once when the user chooses the appropriate option in which a line should be added.