Seems pretty do-able. Perhaps you have to sneak and activate it so you can still sit on them? Would that require a script extender?

Furniture is controlled by settings in the .Nif and has nothing to do with Scripting, all it requires is for a Sleep Furniture Marker to be added to the Couch -> depending on exactly which Couch you can most likely just change an existing Marker from a Sit Marker to a Sleep Marker.

I wonder if you could split a couch and have a sit activator on the right side and a sleep activator on the left side?

It would be pretty cool to be able to either sleep or sit on your couch... I wonder if it can be done...