sending GET data to your report should work, here is an example:
$pdf = $client->ConvertURI("http://your.domain/report.php?year=2010&loc=CE");
You do not need to urlencode your GET data, this is done automatically. If this does not work for you, please add this line before calling ConvertURI().
This will insert the report URL to the footer of the created PDF so you can check which data is passed to your report.
As for the session information, if you mean cookie based session information then it is not possible since we do not support cookies. Session information passed along as GET data is possible though.