Hey DonD,
Thanks for writing in to the forums - I hope your day is going good so far!
The short answer to this is, PingPlotter 5 does not support the script that is needed to make this possible. This feature is on our road-map to be added down the road, but we are unsure of when you could expect this. You *can* get around this by simply disabling one NIC and running a trace (which will force the route through the enabled NIC) - and then you can swap NIC's and run the test again to compare.
Alternately, The ability to do this through a script *is* still available in PingPlotter Pro version 4. If you are absolutely needing this feature, I may suggest downloading and using version 4.
If you do wish to go the version 4 route, here is a guide on how to set everything up for this:
http://www.pingman.com/kb/61If you have any other questions about this (or anything else), feel free to email us anytime at support@pingplotter.com.
Have a great weekend!
-Phillip