using a Rollback Segment for all transactions

I work on a datawarehouse.
I have many transactions which works on multi-threaded sessions.

I try to have all my transaction use a rollback segment which is not always the default one.

Actually I have only found the following command :

        set transaction use rollback segment RBS_DSS;

But Can I do it at the session level ? or for the particular user which runs these transactions (at the time I create this user for example like when I choose the default tablespace) ?

Thanks for all help.

--
bertrand