Hi P KK,
Check the follwing thread http://scn.sap.com/thread/1627557
There are a STANDART SAP JOB that delete this entries. Maybe you can create a varian of this job customizing your retention time.
RSBCS_REORG
Check this sap notes out:
Note 773226 - Deleting transmission requests from the queue delete old records in sosts,
Notes 966854: Reorganization u2013 New Report and 1003894: RSBCS_REORG Corrections.
Cheers.