On Bimmernut we used to have 1 thread dedicated to the jokes for that particular month so there wouldn't be a bunch of threads with them filling up the board.
Basically it looked something like this as the topic
******July Joke Thread*****
and anyone who wanted to add to it comment in it had a one-stop place to go.
Suggest the first person to post a joke for the month make a thread similar, sticky it for the month in general, then bump it off at the end of said month.