Hi Pete,
as you have quite correctly worked out, the HEX-ID field is for your own transponder ICAO, this simply stops PilotAware using either your Mode-S or Mode-S/ES(ADSB) from your own transponder.
Unfortunately there is no way to filter other objects, other than relative height difference in your Nav tool settings.
So the ground items could be filtered once in the air at a relative height greater than your filter.
Interestingly, I recall that ground vehicles have a setting in the DF strings which indicate it is a ground setting, so there is the potential to filter out ALL ground vehicles, could I ask you to add this onto the enhancement requests ?
http://forum.pilotaware.com/index.php/topic,4.0.htmlThx
Lee