Yes, the CellSelectionCallback sounds fine, if you want to apply the operation, when a cell is selected:
function YourCellSelectioncallBack(Source, Event)
Data = get(Source, 'Data');
Data = cat(2, Data, num2cell([2;3;4]));
set(Source, 'Data', Data);
This appends the values 2,3,4 as a new column. I do not know, what "show its values" mean, but this is an example only.