That'll work pretty well, I think.
First draft:
Meld into Carpet (Su?): A carpet snake can enter a rug or carpet large enough to hold its length as a standard action. While inside the carpet, any other designs shift and alter to accommodate the image of the carpet snake that appears where it has merged. A carpet snake is aware of its surroundings using its tremorsense ability. Carpet snakes that have melded with a carpet do not require sustenance for up to a year, but a carpet snake may choose to leave its carpet at any time. This process requires two full rounds. SOMETHING ABOUT ATTACKING CARPET.
Surprise (Ex): A carpet snake melded with the wall receives a +20 circumstance bonus on Hide and Move Silently checks while exiting, often allowing them to surprise intruders.
Should we put some kind of camo ability on while they're melded?