Firstly, to reduce the data set you could do the following, this will make the report more manageable:-
An anlytical function in the universe, if you RDBMS supports it.
DB Rank in Webi query panel, if your RDBMS supports it.
As for the report side, you could look at this for ideas:-
https://bobj-board.org/t/160695
Mak 1 
(BOB member since 2005-01-06)