Is it possible to force a non interactive session into rule based optimizer mode?

The session is started by an application via OCI call to the d/b ? No change to the code for the app is possible, so it would have to be done via procedure/pkg calls. Something like
sql>alter session set optimizer_mode=rule;

The rest of the database can operate in COST based with the parameter optimizer_mode=choose and stats for the tables/indexes.

The application runs as one oracle user/schema.

Any help will be appreciated.