BBH Magicalls - How to replace leg elastic?

I used to dry my medium MagicAlls inside-out and the leg elastic has gone in all of them. I think because the sun damaged it, it went all brown & brittle. I bought them new for DS & he has a skinny butt so he wore the mediums for AGES! DD has been wearing them for a while now too but they leak all the time because the elastic is shot. I love the nappies. I'm hoping to be able to fix them as DD should still fit them for a few more months & they are my favourites, so that leads me to my question for you lovely ladies...

Advice please: Any ideas on how to replace the elastic in the MagicAlls? I really don't want to sew them by hand but can't see any other way besides pulling them apart completely.