Define an argument value for a step in an Oracle job chain

I am creating a job chain in the Oracle (11R2) Scheduler for a DBMS. The chain has two steps. At each step, the same program is executed, but with different arguments. I can understand how to define the chain, steps, rules, etc., but I can not understand how to set the argument values ​​for the steps.

When I create jobs that are single program calls, I set such arguments as follows:

dbms_scheduler.set_job_argument_value(
   job_name    => 'MY_JOB',
   argument_position => 1,
   argument_value => 'foo');  

My question is: what dbms_scheduler func / proc would I call to set the arguments for the job step? Using the examples below, how to set the argument for "STEP_1" to "MY_CHAIN"?

Thanks, John

DBMS_SCHEDULER.CREATE_CHAIN (
    chain_name => 'MY_CHAIN',
    rule_set_name => NULL,
    evaluation_interval => NULL,
    comments => 'Chain calls 2 steps. Same program but with different arg values.');

DBMS_SCHEDULER.DEFINE_CHAIN_STEP (
    chain_name  => 'MY_CHAIN',
    step_name   => 'STEP_1',
    program_name => 'MY_PROGRAM');

DBMS_SCHEDULER.DEFINE_CHAIN_STEP (
    chain_name  => 'MY_CHAIN',
    step_name   => 'STEP_2',
    program_name => 'MY_PROGRAM');

DBMS_SCHEDULER.CREATE_JOB (
    job_name        => 'MY_CHAIN_JOB',
    job_type        => 'CHAIN',
    job_action      => 'MY_CHAIN',
    repeat_interval => 'freq=daily;byhour=12;byminute=0;bysecond=0',
    enabled         => TRUE);