You can try calling QCMDEXC with a ? in front of the command that you want prompted. For example if you wanted to prompt the WRKACTJOB command :-
PARM COMAND 132
PARM 132 LENGTH 155
COMAND is 132 char and contains “? WRKACTJOB”, LENGTH is 15,5 dec and contains 132 (the length of your command string. There should be a space between the ? and the command.
There are better ways of doing this, but this is probably the quickest.