Christian Stocker points out a blog post from Tobias Ebnother showing how to set up a native apache instance on Leopard (OS X) with a 64 bit PHP included.

With massive! help from Marc Ammann I was able to build a PHP Binary that loads with the Leopard shipped Apache.

His method replaces the standard iconv file with a custom built one (based on this source) prior to compiling. Then, in his configure, he sets certain flags, specifically the "arch x86_64" one, to get it to recognize the new setup.