How many IPs did your host provide? If you have at least two IPs then you can use the first IP as your primary nameserver as well as your shared IP, then use the other one for your secondary nameserver. Certainly your host advised you of your IP range?
Edit: I just looked at your host's site. They probably assigned you just one IP for now, but they say they will give another IP with justification. Tell them you need one more IP to use as your secondary nameserver.
Of course, all this is assuming you even want to run your own nameservers.