ss = "waitfor delay '000:02:00' insert into t select 5678"
cn.Execute "exec spAsyncSQL " & Chr(34) & ss & Chr(34)
cn.Close
Set cn = Nothing

Here this user-defined stored procedure spAsyncSQL (tested on 7.0 and
works under running SQL Server Agent):

-- spAsyncSQL Stored Procedure for asynchronous start of T-SQL batch

CREATE PROCEDURE spAsyncSQL @tsql varchar(3200) AS

set nocount on

declare 
  @jname varchar(70), 
  @jobid uniqueidentifier,
  @nt_user_name NVARCHAR(100),
  @dt datetime,
  @itime int,
  @start_date int,
  @skey nchar(1)

set @jobid = NEWID()
set @jname=LTRIM(RTRIM('ZZZ Async T-SQL Batch Executer '+convert(varchar(36),@jobid)))
set @nt_user_name=IsNull(NT_CLIENT(),SUSER_SNAME())
set @skey=N'S'

INSERT INTO msdb.dbo.sysjobs
     (job_id, originating_server, name, enabled, description, start_step_id, category_id,
      owner_sid, notify_level_eventlog, notify_level_email, notify_level_netsend, notify_level_page,
      notify_email_operator_id, notify_netsend_operator_id, notify_page_operator_id,
      delete_level, date_created, date_modified, version_number)
  VALUES 
     (@jobid, N'(LOCAL)', @jname, 1, NULL, 1, 0,
      SUSER_SID(), 2, 0, 0, 0,         0, 0, 0,
      3, GETDATE(), GETDATE(), 1)

INSERT INTO msdb.dbo.sysjobsteps
     (job_id, step_id, step_name, subsystem, command, flags, additional_parameters,
      cmdexec_success_code, on_success_action, on_success_step_id, on_fail_action,
      on_fail_step_id, server, database_name, database_user_name, retry_attempts,
      retry_interval, os_run_priority, output_file_name, last_run_outcome, last_run_duration,
      last_run_retries, last_run_date, last_run_time)
  VALUES 
     (@jobid, 1, 'TheOnlyStep', N'TSQL', @tsql, 0, NULL, 0,
      1, 0, 2, 0, NULL, DB_NAME(), NULL, 0,
      0, -15/*-1*/, NULL, 0, 0,         0, 0, 0)

INSERT INTO msdb.dbo.sysjobservers
     (job_id, server_id, last_run_outcome, last_outcome_message,
      last_run_date, last_run_time, last_run_duration)
  VALUES 
     (@jobid, 0, 5, NULL, 0, 0, 0)
    
IF @@trancount>0 
BEGIN
  set @skey=N'U' 
  set @start_date=datepart(yy,getdate())*10000+datepart(mm,getdate())*100+datepart(dd,getdate())
  set @dt=DateAdd(ss,10,GETDATE()) -- Start after 10 sec. It is needed for the job's cashing.
                                   -- Increase this number if your transactions are very long.
  set @itime = datepart(hh,@dt)*10000+datepart(mi,@dt)*100+datepart(ss,@dt)
  INSERT INTO msdb.dbo.sysjobschedules
     (job_id, name, enabled, freq_type, freq_interval, freq_subday_type, freq_subday_interval,
      freq_relative_interval, freq_recurrence_factor, active_start_date, active_end_date,
      active_start_time, active_end_time, next_run_date, next_run_time)
    VALUES 
     (@jobid, 'TheOnlySchedule', 1, 1, 0, 0, 0,         0, 0, @start_date, 99991231,
      @itime, 235959, 0, 0)
END

EXEC master.dbo.xp_sqlagent_notify N'J', @jobid, NULL, NULL, @skey, @nt_user_name, 0, @@trancount