Using the code below, let me know if you're able to select Aspose from the drop-down in the 1st cell, have it actually display Aspose and then right-click and copy Aspose and paste it to the other 4 columns to the right.
//Accessing the worksheet of the Grid that is currently active
Worksheet sheet = gridDesktop1.GetActiveWorksheet();
//Accessing the location of the cell that is currently in focus
CellLocation cl = sheet.GetFocusedCellLocation();
//Creating an array of items or values that will be added to combobox
string[] items = new string[3];
items[0] = "Aspose";
items[1] = "Aspose.Grid";
items[2] = "Aspose.Grid.Desktop";
object[] values = new string[3];
values[0] = "128";
values[1] = "335";
values[2] = "747";
//Adding combobox to the Controls collection of the Worksheet
sheet.Controls.AddComboBox(0, 0, items, values);
sheet.Controls.AddComboBox(0, 1, items, values);
sheet.Controls.AddComboBox(0, 2, items, values);
sheet.Controls.AddComboBox(0, 3, items, values);
sheet.Controls.AddComboBox(0, 4, items, values);