Last Known Location query

I have a map service set up on tracking observation data. Then I point a customized Time slider widget at this tracking data so that the users can select a Vehicle and see where he traveled during a time period or show all the points where he exceeded 100km/h.

Now they want to know the Last Known Location for all vehicles. The Tracking widget isn't good enough because in some vehicles the gps unit is shut down when the engine is turned off.

So,
1. Can I use a QueryTask with grouping? In sql I'd do something like "select vehicle, max(date) from trackingData group by vehicle".
2. If no to 1 then should I still use the QueryTask with a "order by date DESC" and then set up a custom renderer to only show the first record for each vehicle?
3. Create a database view to handle the query logic, then include the view in the map service and join it to the tracking data somehow?

Any ideas are welcome.

Thanks.
Blaise