Use the following CLI commands:

> enable
# conf t
# ipv6 auto-linklocal disable

The ipv6 auto-linklocal command enables or disables automatic generation of link-local addresses on all interfaces. When this parameter is enabled (as it is by default), individual interface configuration values override this setting. When this setting is disabled, it is disabled for all interfaces (regardless of the per-interface setting). After link-local addresses are generated for the ProxySG interfaces,they will stay configured until they are manually removed using the no ip-address command or until the ProxySG is rebooted.

Or for a specific interface:
SGOS#(config interface interface_number) ipv6 auto-linklocal {enable | disable}

Enables or disables the automatic generation of link-local addresses for this interface.