Proxypass or Irule to load regular http traffic on a https page....is this even possible

Right, so as Mohamed says, something like this:

when HTTP_REQUEST {
    if { [string tolower [HTTP::uri]] starts_with "/brightcovethumb/" } {
        HTTP::uri [string map {"/brightcovethumb/" "/"} [HTTP::uri]]
        HTTP::header replace Host "brightcove.vo.linwd.net"
        pool brightcove_pool
    }
}

You may or may not either need to enable or disable SNAT. You could also, potentially, just change the URI and redirect the user to the real Brightcove server.