Please try this... open the file:
/components/com_dtregister/paypal.class.php
Around line 152 you'll find this code:
$this->add_field('cmd','_xclick');
AFTER that line, add in this code:
$this->add_field('button_subtype','services');
$this->add_field('no_shipping','1');
$this->add_field('bn','PP-BuyNowBF:btn_buynowCC_LG.gif:NonHosted');
This should keep DT Register from adding any shipping to your registrations. Let us know if it works for you. If so, we'll add it to the package. Can't verify for sure because we never had the shipping issue to begin with on any of our sites. Anyway... give it a shot. Thanks.