JIDE's SortableTableModel uses ObjectComparatorManager to get the comparator. You can register your Collator (by default, we use PRIMARY collator)
Collator collator = Collator.getInstance();
collator.setStrength(Collator.SECONDARY);
ObjectComparatorManager.registerComparator(String.class, collator , new ComparatorContext("CollatorSecondary")); // "CollatorSecondary" could be any string that is unique in your app
Then in your SortableTableModel subclass, you return new ComparatorContext("CollatorSecondary") by overriding getColumnComparatorContext(int column) for the column.
Another quick way is to override SortableTableModel's getComparator(int column) if you just want this behavior in one table.
Last but not least, you may also need to call SortableTableModel's setAlwaysUseComparators(true) because for the performance consideration, we used the cell value's compareTo method if available without using a comparator.