As I was taught, KED is the way to get the person down from sitting to supine on the longboard if at all possible, much less risk of tweaking the spine. Don't forget directing your partner to maintain cervical alignment throughout the entire process, and don't forget to pad behind the head before taping it down to maintain alignment. And don't forget CSM before cervical collar and then at the end after transfer to longboard.
Just don't do like I did before correcting myself during the test, all those buckles... go on the OUTSIDE =P My poor victim.
We were also taught the buckles were done in sequence: middle (torso) -> bottom (torso) -> leg straps -> head -> top (torso) (My Baby Looks Hot Tonight mnemonic). It's shown differently in the book so it may be a SoCal protocol.