How do I add a DNSmasq on a TG1682G?
AFAIK, you can't. The 1682 already does a form of DNS forwarding / relay / masking.
I have read in numerous posts online that a Comcast Agent can remotely activate the DNS features. How do I get this?
I'm going to try to get an official Comcast corporate employee that is available to these boards to help you / get an authoritative answer. You should get a reply here in your topic. Good luck !