In order to get rid of air bubbles between cel 
layers, you have to physically separate the cel 
at the area of the bubbles (not necessarily the 
whole cel).  Depending on where the cel the 
layers are stuck, this may or may not be possible.

If there is a clear path between the layers to 
the area in question, you may be able to get rid 
of the bubbles.  I would wrap some tissue around 
a very, very thin rod (thin metal chopsticks are 
perfect) and then try to work your way to the air 
bubble area.  If you're lucky, you may be able to 
get rid of the air bubbles without damaging the 
paint.

Later.