might be worth having a look over:
http://uk.php.net/manual/en/function.http-get-request-body-stream.php

...although a comment note also says that it has probs with multipart/form-data.

Might also be worth having a chat with Zoe Slattery at phplondon if you make it down as she was looking into REST quite a lot recently.

Cheers,
paul