You can totally bring that unplanned, not written on the envelope guest to our wedding. All you need to do is find someone on the list who has already RSVP’d yes and who is non-essential enough to be easily missed the day of (see: work people, estranged cousins). Take him on a Soprano style trip to the river just before the wedding (early enough you have time to wash the blood off but not so early that police will crash the party). Then have your guest steal his escort card (and his escort, if you’d like) and play a little game of make believe all night long. Bonus child invite if your guest wears the invited guy’s face like a mask.