jQuery Grid Plugin - jqGrid

I'm using jqGrid v4.6.0 and I need to change the text that is displayed when using grouping. For example I'm grouping by a case number and I also want to display the case description in the group.  I tried two different approaches:

1) Using a custom formatter on the group field (following the next example that oleg kindly provided)

http://www.ok-soft-gmbh.com/jq.....atter1.htm

2) Using formatDisplayField according to the following example:

http://www.trirand.com/blog/?p.....d-callback

Everything works as expected (I can add some text for example), but if I set hideFirstGroupCol: true the format function is no longer called.

What can I do to get the desired behaviour?

Thanks in advance!