With the aim of using the Reports & Barcode plugin as an export tool (to bypass the page at a time problem), I discovered how to map the path to PHP-CLI. This is required to configure the plugin.
Omeka expects the path to be /usr/bin/php, but in MAMP on Snow Leopard, the path is more complicated: /Applications/MAMP/bin/php/php5.4.4/bin/php
This is similar to the problems with setting paths to ImageMagick, and as with that puzzle, I found the solution by searching directly for MAMP php-cli.
Hope this can help someone.