I used to leave the leader out when rewinding manually but gave up doing so after buying one of the retriever gadgets. There's almost no risk of accidentally reloading an exposed film if you rewind them fully, and it takes seconds to pull the leader back out when I come to process them.
I've done this, more times than I care to remember. It's the main reason I bought duplicates (and triplicates) of my favorite camera bodies.
Peter Marshall: When you pat a dog on its head he will usually wag his tail. What will a goose do?
Paul Lynde: Make him bark.