I added a new plugin for you in the vBSlider plugin area called "Parallax Fix". You should now be able to remove your previous edit to widget.php and it should all work as desired.
I think you were seeing the one loaded from the file edit I did. I currently have the unedited widget file in place so you can see where its loading more easily.
Possibly... Unfortunately, I can't get the new plugin to load after the vBSlider script, no matter what I do. For you right now, I guess go with your option of placing the code inside of widget.php.
For the next version, I will look into adding a hook inside of widget.php at the very end for the specific purpose of being able to place additional code after the slider script.