SQL & PL/SQL

Hi
My problem is that Oracle elects to perform a full table scan when I want it to use an index.
The situation is this: I have a single table SQL query with an IN clause such as:
SELECT EMPNO, ENAME, JOB FROM EMP WHERE ENAME IN (...)

Since this is running in an application, I want to allow the user to provide a list of ENAMES to search. Because IN clauses don't accept bind parameters I've been using the Tom Kyte workaround which relies on setting a bind variable to an array-valued scalar, and then casting this array to be a table of records that the database can handle in an IN clause:
SELECT *
FROM EMP
WHERE ENAME IN (
SELECT *
FROM TABLE(CAST( ? AS TABLE_OF_VARCHAR)))

This resulted in very slow performance due to a full table scan. To test, I ran the SQL in SQL*Plus and provided the IN clause values in the query itself. The explain plan showed it using my index...ok good. But once I changed the IN clause to the 'select * from table...' syntax Oracle went into Full Scan mode. I added an index hint but it didn't change the plan. Has anyone had success using this technique without a full scan?

Thanks
John

p.s.
Please let me know if you think this should be posted on a different forum. Even though my context is a Java app developed with JDev this seemed like a SQL question.