Just in case anyone out there wants to volunteer, the volunteer signup page is linked to from the rundisney page.
Scroll all the way down to the bottom of the page. If you're on mobile, click on see more links. Mobile or computer, go to the Exhibitors and Volunteer section and click on Princess. Log in, sign up. Some things are "sold out", but by no means all.
My cousin and I are participating in the 5&10 this year, and are volunteering to give out medals at the Half. Then doing yoga the next day.
For us, getting the medals is SO important, and we want to make it nice for the people who get them from us.