Although I didn't got this to work, I don't think it can be just a simple css tweak. My skills are realy limited, however I could identify where in the grid.css the table headings (all of them) are aligned and just changed it.

The result wasn't pretty though, as jqGrid reserves space on the heading for the sorting controls so that have to be accounted for… eg perhaps they should revert to the left if right alignment is chosen… And centering the