I put some thought into this suggestion and I have come up with a solution that fits well within the IS framework.

To add an action with several random outcomes do the following:

Make sure you have version 1.09 of Interactive Story (refresh your browser or download v1.09 of the Android app).

Add a new action as usual and when asked to describe the outcome click on the 'random' link next to the submit button.  Confirm you want to create an action with a random outcome.  In the editor there will now appear a new option - [N] Add a random outcome.  Use this option to add as many outcomes as you wish.  The outcomes have all the properties of a regular action.

When reading the story, the IS engine will randomaly pick one of the outcomes located within the same event as the original action.

[EDIT] The original action can now be available to the entire scene (or story if an item only interaction).