Pipe random selection from multiple choice question

Hi there,
We are designing a survey about the curriculum resources teachers use. We are interesting in testing whether the way teachers source and develop curriculum resources depends on the subjects they teach.
We ask teachers the subjects they teach via a multiple choice question in the demographics section at the start of the survey.
Later on, we want teachers to be presented with one of the subjects they teach, chosen at random. Then we are going to ask a suite of questions about that particular subject. We won't do a merge and loop (i.e. we only want to ask about one subject at random from the subjects teachers say they teach).
Is there any way we can do this? I have managed to pipe multiple choice answers into later questions, but can only pipe all selections, rather than one selected choice at random.
Thank you