Hm, then what I described may have been something we'd discussed but have not implemented for FFC quite yet. As a free service offered with no promise of any support whatsoever (technical nor developmental), FFC honestly gets fairly low priority in terms of any resources we dedicate to it, particularly regarding feature enhancements.
An upgrade to E-junkie cart would provide the setting you need but would also require manually configuring products in your Seller Admin here, although you can specify your own custom Item Numbers to make dynamically generating button code at your end more feasible.
Perhaps there's some setting in your PayPal or Google Checkout account that can apply a Shipping fee during checkout, although I'm not certain whether that would be possible if no Shipping fees are being added in the cart before checkout (since usually enabling Shipping in the cart is what triggers address collection during Checkout).
