Woah, that's really something! I know that you'll take great care of him. Hopefully it doesn't slow him down to much. ADFs seem really fragile to me, although I think I've only ever seen babies in person. Do you think there would there be any point in doing prophylactic antibiotics?
I found a very sad American toad outside the wildlife rehab center where I work. It looked like a raccoon had gnawed off all of her limbs. Unfortunately there was nothing I could do to help that. At least I was able to humanely put her down. I can't imagine that quadruple amputee anurans do very well in the wild :/ I'm glad yours has better odds!