However the tweaks I am going to mention are simple and can be used to get this to work. After the tweaks don't forget to build the datavisualization.swc using the steps I have described in one of the earlier posts.
Modifing OLAPCell.as file : Modify the constructor to set a formatted value into the _formattedValue property
public function OLAPCell(value:Number, formattedValue:String=null)
_value = value;
_formattedValue = insert any custom formatting logic using value ;
Modify OLAPDataGrid.as : Somewhere around line 769 we can find the following line
label = cell && !isNaN(cell.value) ? String(cell.value) : defaultCellString;
Modify this to read as follows
label = cell && !isNaN(cell.value) ? String(cell.formattedValue) : defaultCellString;
Build the swc and use it in your app to get custom formatting. Of-course some more tweaking it required to make this generic and supply a Flex formatter directly to OLAPDataGrid. I am sure it can be easily figured out !