Problem with putting a spacer on the door (or track) then becomes what do you do if you ever =need= to remove the doors? Personally, I think I'd put something on the top of the track, screwed into the upper frame, but only as long as the door is. It would be above the doors when in the closed position, then I'd be sure the doors didn't work themselves open. This way, if the doors ever did need to some off, you slide them to the opposite side where you now have room to get them off =and= if necessary, you could unscrew the spacer and remove it, too. JMO...
On edit; is there some way to anchor them to the floor in transport to keep them from bouncing? Even a wedge in the roller track might work. Simple and easily removable. Again, JMO...
Lyle
