you can do "in-memory" sorting.
You could implement it like this:
// get VO and make sure all required rows are fetched from DB
// sort rows by transient attribute
// read current query mode
int oldQueryMode = myVO.getQueryMode();
// perform in-memory sort
// set query mode back to original value (only needed if you want to be able to get new rows from DB)
Hope this helps.
Linda's suggestion is spot on.
Another - less known but declarative - option is to go to the iterator binding in the PageDef file (actually use the binding editor in JDev). Press the "pencil" button on the menu (or the iterator) and switch to the SortCriteria tab. Select "Ascending" or "Descending" based on your initial needs.