Comcast Security Assurance can sometimes "unspam" a sender. You can reach them at 1-888-565-4329 (from http://constantguard.comcast.net/help/report-abuse/). Note that this is NOT one of the general customer service numbers. The first-line reps there are sometimes not very helpful so be persistent and keep at them until you get a satisfactory answer.
Otherwise the only thing you can do is turn off spam filtering completely so that everything they deliver is placed in the Inbox.