How do you have multiple connections to the internet, but the same internet
IP as in 1 internet IP?

The reason I am asking is I want 2 cable modems and 1 ip so I can use both
to increase my download speed. I've got a dual wan router from Sonicwall
that does load balancing etc, but if I go to places online since I have 2
modems I have 2 ips. I want to bind both to 1 ip. Some places online that
you have accounts with to log in will not let you connect with the same log
in on more then 1 ip. So in order to download faster I want to do this so it
sees me as 1 ip.