Partial solution (I think)
In recent version of PHP (ie: more recent than what we have ... don't get me started) you can access $HTTP_RAW_POST_DATA. Earlier versions (like what we have, didn't I tell you not to get me started!) unset this value if PHP recognizes the mime type.
In any case, if I can grab the $HTTP_RAW_POST_DATA value I think I can work with it. Got this answer by reading the source to an xmlrpc implementation.
