iRule for cloned request and response traffic

Give this a shot:

proc send_to_sideband { data server } {
    set sbserver [connect -protocol TCP -timeout 10 -idle 5 -status conn_status $server]
    send -status send_status -timeout 10 $sbserver $data
}
when RULE_INIT {
    set static::sideband_server "10.80.0.200:80"
}
when HTTP_REQUEST {
    set req [HTTP::request]
    set sb [call send_to_sideband $req $static::sideband_server]
}

I'm using a proc here. Not totally necessary, but cool nonetheless. The iRule is basically grabbing the entire HTTP request and passing it the sideband. There's no sideband receive function, so it won't listen for a response. You could alter the request data however required.