Greetings!
When I try HTTP POST on my GSA I'm always redirected to port 80 (and,
more specifically, "home page" mode). Thus, at least from casual
observation, I don't think POST is supported in a search context.
Can you illustrate why POST would be preferred over GET in this case? I
ask because, in terms of best/recommended practices, GET is the
preferred method per the W3C (plus it's bookmarkable to boot).
By contrast, POST is appropriate when a request would "change state" on
the server end.
More info: http://www.w3.org/2001/tag/doc/whenToUseGet.html