Using keyboard controls for Pick Many question

Hello, 

We are really trying to make our e-learning course moving forwards more accessible, including being able to navigate the entire course with just a keyboard. I have been successful so far with most of this but I am really stumped on how to make it work on the free form Pick Many question slides. With the Pick One slides I understand you use the TAB, then arrow keys to go through the multiple choice questions but this does not appear to be the case for Pick Many. 

Any help would be much appreciated, apologies if there is already a thread for this.