@Chris21090 . Exactly! Either your guest wants to pay a significant amount to take it off the STR market now or you really shouldnt offer them this deal unless everyone in your area books at the last minute?
One of the benefits of opening your calendar up is to allow the more reliable and different guests to book ahead. Putting all your eggs in one guest basket is very risky and you would want to have some monetary compensation and protections imo.
Offer him the two weeks and say he is welcome to renew if your place is available.