You simply can't!!! In some situation you can avoid writing transactions to redo logs, but you can't perform transactions without writing undo information to rollbacks.
Undo information is written to rollback segment not just because you might decide to roll back the transaction, but because the database has to provide *read consistent view* for other users on the data you are changing during your transaction! The third reason for writing undo into rollback segs is the ability to perform instance recovery in case database crashes during your transaction.
Bottom line: transactions allways cause undo information to be written to rollback segments, you can't avoid it.
ASCII a stupid question, get a stupid ANSI
24 hours in a day .... 24 beer in a case .... coincidence?