Except for single record FINDs using a RECID ir ROWID the 4GL always uses an index. Even when none is specified the compiler will pick one for you. Usually it does a pretty good job.
Only the SQL-92 engine supports no-index table scans. That feature was introduced, for SQL-92 only, 5 years ago. The db team brags about it every time they get a chance to put up a slide showing what they have done lately.
The 4GL development team has not yet seen fit to support it.
Complain to your sales rep and anyone else whose neck you can reach. Let them know that this is important to you.