The IPS will only update online via its Management IP address , since regular sensor interfaces have no IP address setting option!
You need to default route your traffic from IPS to go to internet cloud and set permission on firewalls or routers to reach the IP address of IPS online databank signature website.
You do not need to have static NAT and , simple dynamic NAT is enough since the inside IPS management IP need not to be exposed or mapped directly and can use random source ports to connect to IPS Global databank over the internet using authenticated and authorized username/password combo which will be fed to the IPS device within the network.
hope this helps.