Help, I have exactly the same problem.
Assuming both screens have a resolution of 800x600, I changed the XPosition in the general.ini in riderunner file from zero to XPosition=800 and the video now appears on the second screen, as do the rest of riderunner apps.
If (using the BMV skin) I place the command /POSX=0 in the external_gps.skin, I get iGuidance in the first screen, however I cannot keep the video displaying in the second screen even though the dualmon=True option does keep the video playing in the background, it visibly vanishes as it switches to the GPS screen.
It seems that whereever the position of the menu screen appears, thats exactly where the video appears.
How can I prevent video from following the /xpos command in the menu screen and how can I keep both GPS and Video displaying at the same time?
I've spent several weeks on this problem so any help would be appreciated.