You can use Virtual Schemas to implement a loading process. Once a virtual schema is defined and the tables of the external data source are visible, an ETL job can materialize these tables using CREATE TABLE materialized_schema.my_table AS SELECT * FROM virtual_schema.my_table statement. You can run complex transformation directly in the subselect. For more information about the virtual schemas, see Virtual Schemas.
If you don't want to materialize all the tables, you can create a mix of views directly to the virtual tables and materialize once and decide which table should be permanently stored in Exasol to get optimum performance.