Redirecting 404 to a friendly page by uri

I'm sorry one more question. What if it was a vanity domain (controlled by host header) on the same VIP that I refer to above. would it work too? something like

when HTTP_REQUEST {
 
      set host [string tolower [HTTP::host]]

      }
when HTTP_RESPONSE {
    switch [HTTP::status] {
  
   "404" {
   switch -glob $host {
    
   "*.vanitydomain.com/*" { 
     
   HTTP::respond 301 \
     
   "Location" "http://www.vanitydomain.com/moved.html" \
     
   "Server" "www.vanitydomain.com"
    
} 
   } 
  } 
 } 
}

I'm not sure if I'm even close on this nor how to stick it in the other irule.

I again really appreciate the help, I'm learning a lot.