Poor Performace when we use Structures in ROWS

Group,

Business users are complaining about BEx query performance.When we analyzed the queries,we found that it is because of the Char Structures under rows.

Example : Instead of pulling the whole G/L account hierarchy in rows,they made a structure in which each and every selection is restricted to one G/L hierarchy node.All together there are 20 selections assigned to one structure.

This is killing the query performance.Are there any tips available to improve this query performance?

Thanks,

Bobby.