9iR2: log which statements use a particular index

Hi,
while trying to reduce the amount of indexes created on some large tables in an OLTP system, I try to figure out which indexes get rarely and what the statements look like that use those indexes.
I know I can monitor index usage, know about v$object_usage and v$sql_plan. What I am trying to accomplish is picking for example five to ten indexes that I know or assume of they get rarely used (but may be very important for particular queries anyway) and log all the statements that use those indexes in some way - to decide wether to drop the index, rearrange it or rearrange the query to use one of the other more frequently used indexes instead.
I thought about setting up a job that regulary checks v$sql_plan (or its base tables) for those indexes and log the statements into a table, as one should not use triggers on system tables etc. - but before reinventing the wheel: Is there a more clever or standard way (avoiding the "best practice" buzzword) to do this? 

Best regards
... Ralph Graulich ...
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