The pdf they link to doesn't outline what the procedure is for those who can't wear a mask. In fact the pdf has this juicy choice quote:
I have difficulty breathing when I wear a mask. Should I still wear one?
Yes, even then you will have to wear a mask. Make sure you use a comfortable model, if possible with an outlet valve to make it easier for you to breath.
Seriously want kind of BS is this? The airline is actually limiting people's ability to breath normally, the world gone mad.