What about util_httppost?
It is in ad_utilties.tcl.preload
from documentation:
<pre>
proc_doc util_httppost {url formvars {timeout 30} {depth 0} {http_referer ""}}
"Returns the result of POSTing to another Web server or -1 if there is an error or timeout. formvars should be in the form "arg1=value1&arg2=value2"
</pre>
This does a post to a URL and returns the contents to the browser.
I was going to use it myself, but my URL I am posting to is HTTPS which does not work.