You can just set your body in CURLOPT_POSTFIELDS
.
Example:
$ch = curl_init();
curl_setopt($ch, CURLOPT_URL, "http://url/url/url" );
curl_setopt($ch, CURLOPT_RETURNTRANSFER, 1 );
curl_setopt($ch, CURLOPT_POST, 1 );
curl_setopt($ch, CURLOPT_POSTFIELDS, "body goes here" );
curl_setopt($ch, CURLOPT_HTTPHEADER, array('Content-Type: text/plain'));
$result=curl_exec ($ch);
Taken from here
Of course, set your own header type, and just do file_get_contents('/path/to/file')
for body.