I have one cat who stretches out into a four legged star when he sees a basket.
I put a small blanket on my knee and wrap the cat in it so his rear paws are under cover and hold his front paws together, have the carrier turned on end so the hole is at the top then drop him in bottom first like a bag of spuds, blanket and all - this stops him swishing his tail into the doorway and gravity helps him stay put long enough for you to shut the door, after that it's just a matter of gently turning the box the right way up so he unwraps himself from the blanket and finds his feet on the bottom.
The trick here of course is getting the box ready first without alerting kit to your evil plans, and don't sweat when you've got the blanket ready - they can smell a plot !