I know I couldn't get work experienence in midwifery so I put a line in my PS about, 'as pregnancy is such an intimate and personal time I have been unable to gain any work experience in this field, however I have spoken to both qualified and student midwives and feel I have gained a good understanding of what the course and career involves.'
Maybe you could do something similar, say the patients are at a vunerable point in their lives or something, but mention you speaking to OTs and your volunteer work