Hmmm... Depending on how they escape this might not work but how about having Aang chained up in a way that partially or completely limits his abilities. Thus they are stuck fighting in close quarters with experienced Firebenders and soldiers while depending on Katara's limited Waterbending abilities. You could imply a parallel between Katara and Zuko's desperate fights for Aang's freedom.

As for how they find the glider.. Why not have them stumble unto it at a desperate moment as a single ray of hope in a dark moment? Or have Aang insist on finding it? It is the last strong link he has to his people including his first family (like Monk Gyasto).