We recommend using VRPN and then you can specify the sensor number when adding a tracker in Vizard. So, to connect to markers 4,7,8 you would do the following (sensor numbers begin at 0)
Code:
vrpn = viz.add('vrpn7.dle')
tracker4 = vrpn.addTracker('PPT0@hostname',3)
tracker7 = vrpn.addTracker('PPT0@hostname',6)
tracker8 = vrpn.addTracker('PPT0@hostname',7)