After several weeks contemplating and scratching my head how the hell those monster bass players manage to play a simple major scale all over the whole neck and make it sound so wicked, I finally managed to work it out. The trick is to basically split the major scale in 5 forms (modes) - ionian, dorian, phrygian, mixolydian, aeolian. I am compiling a doc found here. Check it out. Notice that the order of the modes is always the same. So if I begin on a mixolydian, the next form will always be an aeolian. If I begin on an ionian, the next form will always be a dorian. For any given key, you need to find which is the lowest form and start with it. Example, for the C major scale, the lowest form is G mixolydian.
I will soon post a video of me playing these scales in ascending and descending orders through the entire neck. Needless to say, this is a key exercise for improvisation skills.