That sounds like a feature that Comcast would very likely omit from the crippled firmware that is provided with their Home Networking Service. Best advice is to get rid of the Comcast Home Networking package, buy your own router, and either buy a modem or rent one from Comcast in place of the WCG200 you have now. The router will pay for itself within a year in reduced monthly charges, and you will have a fully functional router with all the features the manufacturer provides.
Do not under any circumstances purchase a combo modem+router gateway!! As soon as you connect it to Comcast's network it will be loaded with Comcast's crippled firmware (All modem devices receive Comcast's firmware.), leaving you in the same situation you are in now, but with the additional disadvantage of owning a completely unsupported router. Because it's Comcast's custom firmware, the manufacturer can't help, and Comcast won't provide help for a customer-owned router.
