USB movies in avi - volume problems

Hi all
I have a usb stick in the front usb slot (i have rear entertainment hence i have a rear usb slot) and i play avi films no problem from it. My problem comes when i switch to duel view and my wife is listening to the movie through her headphones, she has the volume up full on the headphones and when i turn the volume up via the dash it turns the music im listening to up and not the movies volume.
my question is
Is there a way via the dash to turn up the movie volume without turning up the music volume at the same time.
this is a tough question i know perhaps it cannot be done, hopefully some techie will help me out.
Tnx all
Onebigjobby