If you don't get a copy of his or her birth certificate and a well written invitation that includes your full birth name, your social security number, a route description, opening and closing time, a 500 word essay as to what the motivation is of requiring your presence at said birthday, a list of all consumables, planned activities description with according duration times, list of other invitees, and a warning of possible animals that will be present. This all in a well sealed but easily openable envelope of acceptable grade paper. Same goes for the invitation itself, something at the minimum in the vicinity of Bone colored/textured paper with print Sillian Rail. Then you should send an appropriate declination, well according the standards I just set for the invitation, to bring across the message that you will be unable to make a presence as you will be returning some video tapes.