Thinking outside the box here, but I'd be tempted to do this using constructed lists. You'd create a parent list for each CBC task, with three items in the list. Each item would include the code you posted in your comment, but would specifically be coded for task x concept 1, task x concept 2, and task x concept 3. To randomly display a non-selected one, create a constructed list that adds the parent list, removes the selected option, and then randomizes the list:
Parent List: ListCBCTask1
Constructed List: ListCBCTask1NC
Then just display the ListLabel for the first item, which will be a randomly selected unchosen option.