It doesn't have to be that hard :-). If you are married and the two of you want to each give a gift to your son without filing a gift tax return (greater than the single gift limit but under the double limit,) just write your son a note that you are each giving him part of the money and both sign it and keep a copy in your records. It can even be an email chain that you save or print out.
Not only will this satisfy the IRS, but they will never audit you about this anyway. It's far from the top of their figuratively piled high desk :-).
