Utilize Cluster Key To Ensure Uniqueness / Primary Key Constraint

I am trying to add a primary key constraint to a cluster table on the cluster key columns whitout creating additional indexes.

Example:

CREATE CLUSTER CL1
(A NUMBER)
SIZE 100;

CREATE UNIQUE INDEX CICL1 ON CLUSTER CL1;
gives

ORA-01715: UNIQUE may not be used with a cluster index

CREATE INDEX CICL1 ON CLUSTER CL1;

CREATE TABLE CLT1 (A NUMBER,B NUMBER,primary key (A) using index cicl1) CLUSTER CL1 (A)
gives

ORA-14196: Specified index cannot be used to enforce the constraint.

CREATE TABLE CLT1 (A NUMBER,B NUMBER, primary key (A)) CLUSTER CL1 (A)

creates an additional system generated index SYS_C....

Is there any way to utilize the cluster key to ensure the uniqueness/primary key constraint of the cluster key columns of table CLT1 ?