David,

I completely agree. That's what I said it would be considered an ugly hack. Your solution using iptables is probably the most efficient on Linux. On other platforms, or if we want something portable, we could use one of several small daemons that can handle this task like rinetd  or redir or if want to get into trouble, a swiss army knife like netcat or socat :)

http://www.boutell.com/rinetd/
http://www.bigsoft.co.uk/blog/index.php/2010/06/22/building-redir-redir-c-from-patched-sources