Version 0.6.3 of the Google API php Client appears to support the importRows command:
public function importRows($tableId, $optParams = array()) { $params
I know this is a late reply, but for future reference, I will reply it anyway: You need to use the uploadType, mimeType and data on the optParams array.
Example:
importRows( [tableId], array( 'uploadType' => 'media' , 'mimeType' => 'application/octet-stream' , 'data'=>'1,Moth, 30, 2012') );