Maybe they had it before, but I just noticed this today, that we can install more than one versions of PHP, and then use eselect to switch the version.
In short, we can set in /etc/make.conf:
PHP_TARGETS="php5-3 php-5-2"
PHP_INI_VERSION=production
Then call eselect to see what php versions we have available in apache:
# eselect php list apache2
Without "PHP_INI_VERSION=production", a dev version of php.ini will be installed.