Using the standard characer, I have used the "climbing" animation. I'm not sure what the numeric designation to use, however. You have to do a lot of tweaking to get it to look right and of course there is no particular animation for the npc to do anything while sitting. Also, you will never get the npc to look perfect using this animation.
Tax78 is good at adding custom animations. He has added two sitting animations for me on an npc. Contact him and he will give you a quote. He is very reasonable cost-wise. I plan on having him do more work for me.
I'm addicted to programming and coffee!