I'm not sure whether it's even possible to do this, but I would like to offer my customers a choice between getting free shipping on orders over a certain amount, or getting a specific product for free. I've looked at various ways it might be set up, and don't see anything obvious. Has anyone else done something like this and have any suggestions?

Seems like this has good potential for a marketing plugin, if it's not possible to do it directly in Zencart.