I also am on hold for 2 hours and they keep telling me that I need buisness account or a second cable modem to get an additional ip address.
I have a Arris T25 who do I talk to get a second address.
First, check the "Rate Card" for your local area to see if that feature is even available anymore. Seems that it is being phased out;
It's a PDF.
Scroll down to "Xfinity Internet" and look for "Additional IP Addresses".
If nothing is listed then it's likely to have been discontinued in your local market area.