You should be able to issue the show tech command from the Device.CLI.Send Commands activity.
If you wanted to do this as part of the backup activity then on the options pane for the activity you can tick the 'Use alternate command box' and enter Show Tech in here.
A couple of thing to note for this are;
1) It will then issue the Show Tech but not the show running.
2) The alternate command will be used for every device in the activity.
If you are trying to backup information from different contexts then you will need to session into the contexts, treating each like a separate device. Please see the link below for more details;
If I have totally misunderstood what you are trying to do please elaborate.