Two word for you:
Starch Retrogradation. This is the major contributor to staleness. I would ask why you have to keep them on the shelves for 7 days, and whether they sit on a grocery shelf or your kitchen counter
You have two major options:
1) Control the environment
In otherwords, packaging. You can package them using special film. Your other aternative is to freeze the cookies.
2) Use a modified food starch
Depending on the situation, guargum might or might not work. Most of the major cookie companies use a proprietary starch made by people like Staley, ADM, or Cargill. If you're interested I can give you some contacts.
Kuan