What is the real need, for buying a second block of ip addresses, Are you assigning these public IP to your worstations ? You can make your workstations access the internet, by using a single IP address. You dont really need these many IP addresses, unless you have any Public Access servers.
To add the second address, you can use
ip add 216.x.x.x.x 255.255.255.240 ----- this is primary
ip add 64.x.x.x 255.255.255.240 secondary
Use the second statement with "secondary" keyword, so that the ip address will be added to your ethernet interface.
UC Solutions Architect
Pacific Northwest | CDW
CCIE Collaboration #17135 Emeritus