Note to self: use a RewriteCond against %{QUERY_STRING} to match Query_String arguments in RewriteRule’s. To send requests for http://www.example.com/stuff.jsp?id=2 to another host:
RewriteEngine on
RewriteCond %{QUERY_STRING} id=2
RewriteRule ^/stuff.jsp http://www.acme.com [R,L]