How to create iRule to deliver an alternate page response other than 'page unavailable'

Here's what we use on our public web sites. Stored the HTML and images in iFiles for use elsewhere.

when HTTP_REQUEST {
   if {[active_members [LB::server pool]] < 1} {
      switch [HTTP::uri] {
         "/guardian_header.jpg" { HTTP::respond 200 content [ifile get "guardian_header_jpg"] }
         "/guardian_logo.jpg" { HTTP::respond 200 content [ifile get "guardian_logo_jpg"] }
         default { HTTP::respond 200 content [ifile get "maint_index_html"] }
      }
   }
}