Respond to Get request on it's own?

Sure. Use an iRule. Just implement the HTTP_REQUEST method, check the URI sent, if it's the specified string, respond to it from the iRule, if not just continue to forward the request as normal.

e.g. (Sorry, quick cut & paste from another iRUle, but the gist is there. It looks up the URI in a data group and responds with the content (value) if it exists).

when HTTP_REQUEST {
   Retrieve the login form from a base64 encoded external class file
   Pull just the filename from the path... So we need to get rid of the leading '/'.
  set lf_file [substr [HTTP::path] 1]
  if { $lf_debugFlag  >=2 } {
HSL::send $lfs001hsl "${lfs001HSLPrefix}:: Checking for $lf_file in DG $lf_contentClass"
  }
  
  v9 set lf_ResponseData [findclass $lf_file $::loginForm_test " "]
  set lf_ResponseData [class search -value $lf_contentClass equals "$lf_file"]
  if { $lf_ResponseData ne "" } {  
   There's 2 fields... 
    set lf_MimeType [getfield $lf_ResponseData " " 1]
    set lf_Content [b64decode [getfield $lf_ResponseData " " 2]]

    if { $lf_debugFlag  >=2 } {
  HSL::send $lfs001hsl "${lfs001HSLPrefix}:: Serving $lf_MimeType for $lf_file"
    }
 Perform the substitutions...
if { $lf_MimeType equals "text/html" } {
      regsub -all {} $lf_Content "[IP::client_addr]" lf_Content
    }
 
    HTTP::respond 200 content $lf_Content "Content-Type" "$lf_MimeType"

}

H