SQL*loader performance and indices

Hello. I am working on an app which may be inserting tens of millions of rows into couple of tables (oracle 11.1). I want to use a SQL*Loader to load the data but I have the following restrictions

- the tables are in an OLTP database so the tables need to be accessable during the load

- the disk space is limited

My usual approach is to use a staging tables to combine the data currently in the base table append the new data via SQL*Loader in direct mode, rebuild inidices and exchange the stage table with the data in the base table via alter table exchange partition. However, I may not be able to get extra disk space to accomplish that. If I were to load the data directly into the base table, I need to keep the indices to allow this table to be read while the load is running. I thought that direct load won't even work in this situation? Am I correct? If so, what