HTTP Re-Direct with html holding page

Give this a shot.

when HTTP_REQUEST {
        if { [TCP::local_port] eq "80"  } {
            persist source_addr 1800
            HTTP::fallback http://support.com/
            set dtime 3
 Un-comment the next 3 lines for redirects and expand out with elseif's if needed 
               if { [HTTP::host] == "www.domain.co.uk" or "www.domain.com" or "www.domain.org" } {
                HTTP::respond 200 content \
"Apology page\
We are sorry, but the site you are looking for is temporarily out of service." "Content-Type" "text/html" 
            } else {
            pool Web_Farm_Front
 Un-comment the net line if using redirects            
           }
        }   elseif { [TCP::local_port] eq "443"  } {
            HTTP::header insert "BPL-SSL" "On"
            pool Web_Farm_Front
        } else {
        set srvr [findclass [TCP::local_port] $::Individual_Servers " "]
        if { $srvr ne "" } {
           node $srvr 80
        }  else {
 Replace HTTP://sitename with the default URL of the site
          HTTP::redirect "http://www.domain.net/"
      }
   }  
}

I borrowed logic from the LTM Lite Maint Page.

http://devcentral.f5.com/wiki/default.aspx/iRules/LTMMaintenancePageLite.html

I haven't tested the above so wouldn't be surprised if it didn't need a tweek or 2.