STREAM_MATCHED for regexp replace ?

 
 when HTTP_REQUEST { 
  
     Check if the client used a host header 
    if {[string length [HTTP::host]]}{ 
       set host [HTTP::host] 
    } else { 
        Use the VIP address instead 
       set host [IP::local_addr] 
    } 
 } 
 when HTTP_RESPONSE { 
  
     Check if the response was a 200 and text 
    if {[HTTP::status] == 200 and [HTTP::header "Content-Type"] contains "text"} { 
       STREAM::expression "@'/images/@'http://media\.$host\.com/images/@" 
       STREAM::enable 
    } 
       STREAM::disable 
    } 
 }