I think it is pretty clear that Toyota doesn't want you to do it (and I won't be trying it). (See the last page of the emergency manual for example where it doesn't make any mention of this:
http://techinfo.toyota.com/public/main/CamryHVerg1.pdf)
But, from what I know about the 12V converter under the hood, it could work.....
but I think this is definitely in the category of .... don't try this at home.