I want to fly my Shih Ztu from Seattle, WA to ATL?

It will be a tight fit for him and he will fill up the carrier not super snug but he won't be able to turn around. I think I will take him to the vet and get him a tranquilizer for the trip. What do you think ? Cruel ? I moved to ATL and din't bring him cuz I wasn't sure I was staying now I am staying and want him here. Airline says if he don't fit under the seat he cannot come on the airplane thus no other options that I know of unless I want to drive him here which will kill both of us.