Step one will be to find or write a useable PHP Kafka Client.
I hacked on a possible PHP Kafka client at the Wikimania Hackathon. Doesn't look easy! I made a short attempt at HHVMizing https://github.com/EVODelavega/phpkafka, and failed. The other options is the native PHP https://github.com/nmred/kafka-php. However, it has a PHP C Zookeeper extension dependency.
We don't need Zookeeper to produce messages to Kafka. kafka-php uses it in the produce logic because it was written for a slightly older version of Kafka. It should be possible to fork kafka-php and edit out any of the zookeeper dependencies if we plan on using it only for producing messages.