An old idea triggered by a chat on fetlife:

1) A dunking stool setup, pond, etc with some minor changes. The dunking
stool has an open bottom like a toilet seat. There is a small camp fire
on the bank of the pond. The dunkee first gets dropped on the camp fire
and then gets dunked in the pond and them back to the camp fire until
the camp fire is out ;)

2) Instead of a camp fire there is a bunch of thumb tacks. The dunkee is
dropped on the thumb tacks and then placed at a removal station for their
removal. This is repeated until all the thumbtacks have been moved. the
thumb tacks might even be on a long bench seat so it could take some time.