Curt makes hitches for all Scions, and Hitchsource is a web vendor of Curt hitches. Here is the one for the tC:
http://www.hitchsource.com/select.php
You could use the "contact us" feature of their page to ask Hitchsource your question, or call them:
Hitch Source LLC
16055 SW Walker Rd #256
Beaverton, OR 97006
Phone: 877-464-4824
Fax: 866-771-3981