As the seller of a firearm, if you want a NICS check done on the buyer, you must go with the buyer to a FFL dealer (who is willing to do it) and have them handle the NICS check. I believe the Form 4473 is completed also as part of the transaction. That would be retained by the FFL dealer. You would have to speak to a FFL dealer as to the specific details and how to's or what if's. There obviously will be a fee and I suspect it would be something consistant with transfers done for online gun sales where the firearm is shipped to the dealer and then transferred to the buyer.