The above method has also been documented in the FileMaker Training Series.
It's effective if you can work within it's limitations.
An alternative is to create several copies of the same portal, but with different sort orders. These portals can be placed on different tabs of a tab control or on different layout. Clickint a button or selecting a value from a drop down can perform a script that then selects the appropriate tab or layout for the specified sort order and field.
It can be very labor intensive, but sometimes is the only way to get the desired sort order.