Well, ...

1. On your dnn portal create new security role “StoreManager”. This role allows non-admin user (from dnn app viewpoint) manage your store module.
2. In WebControls project locate CustomerOrders control and open CustomerOrders.ascx.cs file. Search for showOrderDetails function and locate the following fragment of code:

   if (UserInfo.IsSuperUser || CheckForAdminRole())
   {
   …
   }
   else
   {
   …
   }

3. Change if statement condition as follows:

   if (UserInfo.IsSuperUser || CheckForAdminRole() || CheckForStoreManagerRole())

4. Copy somewhere the following implementation of function CheckForStoreManagerRole:

   private bool CheckForStoreManagerRole()
   {
       DotNetNuke.Security.Roles.RoleController roleController = new DotNetNuke.Security.Roles.RoleController();
       ArrayList roles = roleController.GetUserRolesByRoleName(PortalId, "StoreManager");
       foreach (UserRoleInfo userRoleInfo in roles)
       {
           if (userRoleInfo.UserID == UserId)
           {
               return true;
           }
       }

       return false;
   }

5. Rebuild, enjoy.