jQuery Grid Plugin - jqGrid

I want to allow deleting rows in a grid generally but prevent it for specific rows (based on data in the row).

My grid displays billable items whether they have already been invoiced or not. A user can choose to delete an item unless it has been invoiced. So my grid allows deleting and the normal button (not a custom one) appears on the navigation bar.

When the delete button is clicked, if the invoice field is not empty, I want to show an dialogue of "Can't Delete blah blah" instead of "Delete selected row?" and I then want to prevent deletion.

Is this possible Tony?

Thanks

Reg