Yeah, the @sit_place thing is a pretty good idea. I remember (quite some time ago), roleplaying on GOLD and sitting along side the road in one of the parks there through poses. A Judge came along and told me to "get out of the road" and much confusion ensued. So it would be good to do something about that.. however..
If you want to be technical about it, you can already make it look like you're sitting somewhere specific if you use @look_place. However, there are some things that can be done while doing this (i.e. combat, walking, etc.) that you can't do when using the actual sitting command.
Whee.