dynamic ips

Cox offer something called multiple computer access, which for a fee allows you additional DHCP IPs. I do not know how much it costs,the only information I can find is here.  

"Learn about Multiple Computer Access and the steps for adding an additional computer to the Cox High Speed Internet service. For Home Networking from Cox, see About Home Networking"

This is another example of the Cox support site being broken since recent change. Could Multiple Computer Access (MCA) info and pricing be confirmed?

Out of curiosity, why do you need the second IP? Is it for a security camera or something similar? I only ask because their may be a easier work around.

You can have up to 3 total.  Sign into your account at http://www.cox.com and click Internet Tools to order.  There is a one time $9.99 setup fee and additional IP's cost $6.99 each.