title: How can one set a variable for use only during a certain dag_run
body: <p>How do I set a variable for use during a particular dag_run.  I'm aware of setting values in xcom, but not all the operators that I use has xcom support.  I also would not like to store the value into the Variables datastore, in case another dag run begins while the current one is running, that need to store different values.</p>